Aiseesoft Blu-Ray Copy seems a nice app, though I have one warning & add several caveats that have to do with the Blu-Ray format itself [rather than the Blu-Ray Copy app]. Primarily it's job is to copy the contents from a Blu-Ray disc to your hard drive, though it does offer options to make that content smaller to fit on a 25 GB BD writable disc, & it does have the capability to burn that disc for you.
The sole warning comes from Aiseesoft Blu-Ray apps adding a hacked driver to XP [& possibly Vista] so the OS recognizes Blu-Ray format discs -- I've tried getting around it in the past but their install is coded right into the Aiseesoft apps, & triggered whenever those apps run. The hacked driver's been around for a while, didn't work for me in XP Pro, & some folks report having problems because of it. For me the solution was a combo of updates from Microsoft + the version of PowerDVD that came with my Blu-Ray drive. Now for the caveats, to help you decide whether or not you want to bother backing up the Blu-Ray discs you've bought...
Once you open Aiseesoft Blu-Ray Copy you can select the source [a Blu-Ray disc, folder, or ISO] & destination, then choose to copy the entire disc, the main movie, or clone the disc. Blu-Ray discs come in 2 sizes [single layer & dual layer, just like DVDs], but be prepared for a shock if you've never priced a dual layer writeable BD disc before [they've come down in price considerably, with a single disc dropping from the $50 range to close to $20 on Newegg] -- for comparison single layer discs can be found for a bit under $1 each. Today's GOTD lets you select either 25 GB or 50 GB for output, but selecting 25 GB when the original disc is larger than that brings up added issues.
Perhaps the most obvious way to reduce the overall size, so it might fit on a 25 GB blank disc, would be to copy just the main movie -- however Blu-Ray Copy wouldn't let me select just the audio tracks I wanted [the grayed out checkboxes might hint this is coming in a future version]. The DTS audio track for a movie can be 1GB+, so skipping a language you don't want or need can save a useful amount of space. But also note that Blu-Ray DRM may include fake titles, so if you or Blu-Ray Copy select the wrong one, well try, try again -- it may be useful to copy the entire disc to your hard drive, then copy just the movie from that Blu-Ray folder... it would obviously take longer to copy the entire disc, then copy the movie too, but once on your hard drive, copying just the movie happens much faster [your hard drive reads Much faster than your Blu-Ray drive]. When you have the choice of 2 or more titles that appear identical, the best way to tell that you've got the right one is to watch it -- re-writable Blu-Ray discs aren't expensive, but they often take longer to burn, while many software players will not play Blu-Ray from a folder on your hard drive. If you've got a Very long list of possible titles, you might get tired of the movie before you find the right one.
If you select the 25GB output when the original disc or movie is bigger than that, Aiseesoft Blu-Ray Copy can re-encode the video to make it smaller. One potential issue is the [usually Java] Menus on the original disc -- If Aiseesoft Blu-Ray Copy can handle them so they still work afterward [which would be a bit rare], it's SLOW -- leave the PC running full tilt over night slow... I realized that if I completed the test I wouldn't be able to give you the results today. Naturally your mileage may vary, & re-encoding might be faster if for example it uses the available Cuda acceleration with your Nvidia graphics card. The slowness isn't because Blu-Ray Copy is poorly written -- it uses ffmpeg, which itself uses x264 for Blu-Ray AVC format video, & while x264 is great, at higher quality settings it's watch the grass grow slow [for comparison, encoding Blu-Ray AVC in some software happens much closer to real time speeds, i.e. 24 fps for 24 fps video so that an hour of video takes an hour to encode, and encoding Blu-Ray mpg2 is faster yet].
Many Blu-Ray discs you buy include DTS audio, often 7.1 [8 channels with a 5.1 mixdown included], & Aiseesoft Blu-Ray Copy will let you strip out the HD audio part &/or convert it to AC3. That saves space & may sound better through your HDTV speakers, but if you tend to be more of an audio purist you may not be happy with the results. The original DTS may have a large dynamic range [the difference between loudest & quietest], & often the dialog is somewhat suppressed so it's hard to hear & understand what people are saying -- automatic conversions can tend to be a bit loud across the board, with IMHO too much of the dynamic range removed so it sounds a bit flat.
That all said, if you copy the main movie or a complete Blu-Ray disc to your hard drive, the free BluRip will give you the original individual video, audio, & subtitle files contained in the Blu-Ray disc. The mkv video file can be re-encoded if or as you need, & the free multiAVCHD will put everything back in Blu-Ray format you can burn using the free Imgburn. If instead you're interested in converting a movie on Blu-Ray to something else, use one of the converters/rippers & you can skip that BluRip step.
The GOTD serial number or key won't work with anything but the GOTD download, so I'd be more inclined to think you won't be able to update Aiseesoft Blu-Ray Copy. Installation adds/uses a Aiseesoft key in HKCU [32 & 64 bit Windows], includes the program's folder, a folder in (My) Documents, a folder in Program Data [All Users\ Application Data in XP], & a Log folder in UserName\ AppData\ Roaming [UserName\ Application Data in XP]. Blu-Ray Copy phones home, I assume for info on decrypting the disc -- like competing apps it's impossible to know if it'll handle every disc today &/or next year -- can't know if the decryption info will be updated tomorrow or indefinitely into the future.
You'll have to decide for yourself what the odds are any Blu-Ray discs you've bought might become damaged & unusable -- IMHO they're more easily damaged than DVDs -- & if the investment in time & money is worth it. Considering you can use a Blu-Ray drive in your PC for other stuff, like backups, & Blu-Ray Copy is on GOTD, I think of it as fairly reasonable insurance.