I have found the whole system to be very slow too, signing in and changing pages takes far longer than it should which suggests that the CAA are running it all off a single/old Server, which will be an issue during peak booking times, probably around 2 weeks prior to each sitting. When it does work, it is pretty good, straight forward booking a slot although I do remember a small issue with remembering which exam I had put where but that was fixed with the confirmation emails sent out afterwards.
Besides those issues, the exams themselves are very good, well explained in how to progress through them, loads of space at each exam station, and comfy seats. Secured lockers just outside of the exam room are also fantastic but they are a little bit small, say if you have a bag and a Jep manual, you will have to squeeze your bag down to get them both in, it is possible but a bit of a pain.
One issue I did find when doing the exams was that if you want to add notes for contesting there is no way to edit or remove them after you have typed in and then clicked elsewhere. Clicking the note button again just adds another note in the top left.
Other than those issues, I'm very happy with the e-exam process.