Hi PB2,
had you ever had a vasectomy (the snip)? If not, you have now had it done as part of your op and if you ask any of your mates who have had the snip they will probably recall pain in the scrotum being one of the side effects. Everything has been shifted and mucked about so pain and twinges should not be a surprise.
As for the trial, it depends on your liking for a bit of a wager I think. I have never been in a betting shop in my life but others love the thrill. With a post-op PSA of almost 0.1 you could enter the trial on a 'just in case' basis but have to be prepared for the possibility that you are going to have unnecessary treatment with unnecessary side effects. Alternatively, you could decline the trial but then find your PSA starts to climb and you end up with salvage treatment.
Talk to the oncologist - ask exactly why the trial was suggested to you, what the different arms are and what happens if you go on the trial but it becomes clear later that you need the option that was another arm.