Having gone ahead with getting MapleTA hosted by Maplesoft, I will answer my own question for the benefit of other people considering this move.
The link is excellent and we have run online exams for over a hundred students. There was no loading delay apparent. There have always been small glitches in the operation of TA and we have raised these with Maplesoft. Usually log files have to be sent. Now we simply relay the problem and Maplesoft support investigate on their own server resulting in much less. Much more convenient! One downside is that, if you have a support contract, it does not run on a 24hour basis. This can be important where immediate support is required such as during an online exam. There is no technician on the other end of the phoneline if it is during the Canadian night! This is an issue which needs addressing. (This summer one of the support technicians gave me his number and indicated he would help if there were an emergency during our exams taking place in the Canadian night! I stress this was unofficial and we were very grateful. We did not need to call him.)