I only found a little bug when choosing install location of new java apps.
Opera Mini works perfectly, speed is not better or worse, but i believe rendering got a little slower (some 3d games got a little fps drop, not much though)
Tested most of Java API's available - JSR's 184, 172, 82, 226, 234 - and all worked fine (didn't tested JSR 256 Sensor API - and bluetooth was not exacly tested since i don't have 2 devices, but didn't crashed)
Jbenchmark shows a nice user experience performance, with some lacks in 3d and 2d rendering (i guess having a bigger screen has some disadvantages).
However, be advised to reinstalls java apps and install new java apps into memory card, or else you will end up having memory issues. That said, make sure you also have enough phone memory when installing this JRE.
A very nice work, but it should be possible for the user to convert the old java apps into memory card and not into phone memory, or at the very least assure that there is enough memory for the device work correctly.