As a driver trainer who in the past has used Exeter for LGV driving tests, however I would not recommend it!
There is a major road that has a very unusual set of bus lanes, some of which are clearly signed with a lorry symbol allowing use by any LGV over 7.5t, and further along this road there is a 24 hour bus only lane. In a test situation trainees often just follow the cars and stay out of the LGV bus lane or use it and then also use the bus only lane!
Also at the A38 (Marsh Barton) signal controlled roundabout, turning right is very tricky in an LGV due to the closely spaced traffic lights and keep clear areas.
At the test centre the reversing bay is very close to site boundary fences and this presents additional stress.
I would suggest you either travel to Peter Symthe’s excellent facility of have a look at MT Training who have recently expanded into Plymouth.
The roads in Plymouth are very free flowing with generous widths and consequently on a driving test it is rare to meet busy traffic.
Good luck with your training and test.