If you have not already searched, you can find a few threads on this site about the 2394 & 2395, including pass rates for the written and practical exams.
For the written exams, the common multiple guess (a pass for this counts for both 2394 and 2395) is not so hard, but the separate main written papers (usually on consecutive days for 2394 and 2395) are indeed challenging for many, and the pass rates are not that high (they do vary a bit, perhaps the level of the papers is not that consistent).
For the practical exams, I think this depends a bit on how strict/helpful the tutor is - shall we say some are doing their best for you to succeed, while others are not so accommodating. You do need to proceed safely, if you are about to do something dangerous, the tutor supervising will terminate the session. Apart from that, the main problem is working efficiently, it is very easy to run out of time. You could build yourself up your own test board - you can make it look quite like the C&G 2395 one - and practice on it, it will help.