It's definitely worth £500 to me - I think that a normal JRE-distribution would cost me approximately 95% of my sales. That's a good trade.
Now, treading on thin ice but unafraid to don my flameproof pants as usual*, I'd like to stick up for what Jet actually offers:
1) Incredibly quick startup time. Whoosh, it's loaded. It's at least twice as fast as the client VM and about 10x as fast as the server VM to load Alien Flux. This makes A.F look a lot more professional; again, I think this will probably translate into sales. Even if it only translates into 50 sales I've easily made my money back.
2) As I've moaned before, the client VM isn't fast enough - it requires a machine about 20-50% more powerful to achieve the same performance as the server VM. This translates to requiring a minimum spec that's 20-50% higher, which correspondingly translates again into a big loss in sales. I can run A.F. on a P200 (albeit with lo-res graphics, 16 bit color and 30Hz) using Jet. The client VM needs a much tidier spec.
3) Unfortunately the server VM, whilst being as fast as hell to run, is slow as hell starting up. It looks awful. The Jet exe, on the other hand, starts instantly at full speed, no glitches. Again, this will translate into lost sales.
4) The server VM isn't the default VM anyway
5) I have a suspicion that garbage collection is even faster in Jet than the server VM. YMMV. Escape analysis appears to have done away with the few inconsequential instantiations I do; and an advanced incremental concurrent collector with capped execution time
has ensured that there are literally no GC pauses. Looks pro. The only pauses you get in A.F. are when it has to load something from disk.
6) Robustness. The whole game is a single .exe, easily installed and run by a total idiot. They can't break the JRE somehow either, as there isn't one.
All the other differences between running with Jet and a JRE aren't terribly relevant to me, like reduced memory consumption etc etc. It just does what it says it does and it does it extraordinarily well. You get what you pay for.
*burn, then drown, baby