Jon don't worry about them, if you ride in the 17s you'll be fine on any reliability trial.
There are some fast guys and gals out there who use them as early season race prep, there are some fast club riders who may have a blast round, there are also a fair few who use them more as they used to be and just have a nice ride around the countryside. It's a great way to see new bits of the near countryside that you don't always ride in. Addiscombe or not you'll find some people of a similar speed and can have a good ride round with them and a good chat.
This Sunday's is run by a club that has a lot of tricycle riders so you'll probably see a few old fellas going round on their trikes
. Don't laugh though as some of them
are still pretty quick.
If you ride out with other Addiscombe riders you can always arrange to ride back together as well. So long as you don't go round hours slower than everyone else, and I'm sure you won't, you can meet up at the HQ after. They'll just have a chance for an extra cup of tea and cake than you that's all.