The GPU version being a superset of the CPU version, what applies to JCE CPU also applies to JCE GPU, notably the netcode, the forks or the security concerns, please take a look at the CPU only version.

The 0.33b8 and later offers a speed increase in most cases and a more stable hashrate, you're advised to upgrade even if you didn't experience problems on older versions. The 0.33b11+ is recommended.

Limitations

Minimum system is Windows 8.1 x64, Windows 7 is not supported.
No 32-bits version
No Linux version
No support of nVidia GPU
APU (even AMD ones) were reported to cause problems
Limited support of Intel IGP/GPU

Speed

It's hard to compare GPU Miners. There are a lot of external parameters: the card itself, its memory, the biosmod, the drivers, the overclocking, the Power Limit...

However, according to the first feedbacks, here's the status on CN-v7:

JCE is faster than any other miner on small RX cards (RX550 and RX560). They are my favorite cards, and the ones I use on most of my rigs.
JCE is always faster than the Wolf0-based miners (Stak, Xmrig, Gateless...). This is not fair since I can read their code and they cannot read mine, but it's a proof JCE is not a copy-paste of their code.
JCE is surprisingly fast on Vega, reaching 2050+ on Vega 64 on CN-v7.
JCE is close to SRB and Claymore otherwise, sometimes slightly above, sometimes slightly below.
I got mixed results on HD7800. I measured higher hashrate than other miners on my rig, but got opposite comments from some users. To be tested.
JCE is bad on small 1G cards compared to the legendary Claymore 9.7, but this miner is no longer supported.

On CN-v8:

Still always better than the open-source miners (Stak, Xmrig, Gateless...).
Claymore is just no longer compatible.
JCE is the best on older cards like HD6000 and HD7000 and R7/R9 series
RX560 cards reach 500+, 850+ on R9 290/X, RX570/580 cards reach 1000+
420+ on HD7850 2G
480+ on HD7950 3G

On CN-Heavy/HVX/Tube:

JCE is faster than the open-source miners on most cards:
1750+ on Vega56
1025+ on RX570/580 4G
1200+ on RX580 8G
330+ on HD7870 2G
425+ on HD7950 3G
The CPU part of JCE-GPU is the exact same than the CPU-only version.

Fees

0.9% for the GPUs
1.5% for the AES CPUs
3.0% for the non-AES CPUs
If you mix CPU and GPU, fees are adjusted proportionally.
If you mine with GPU only, disable CPU mining with --no-cpu or manually configure zero CPU, rather than pausing your CPU to avoid paying CPU related fees for nothing, and vice-versa.

End of development

Due to lack of dev time to provide legit implementations of the new forks (read: not just a rip of the reference code), I had to end the dev. The forks listed below are the last to be supported and notably Monero4 isn't and won't be supported. The miner itself can still be used, with good performance, on the supported forks, including BitTube, Stellite v8 and Turtle v2.