I'm taking 6-MP since almost 6 weeks and so far, I am very happy with it.
Before taking 6-MP, I was on Pred for the first time for almost three months and it didn't do really anything for me. I stopped Pred after being on 6-MP for two weeks. I am in remission now since around 3 weeks, that means I have no symptoms, one or two normal BMs in the morning, no blood, no mucus, no urgency, no pain. A colonoscopy might show still inflammation (gonna schedule my next scope next week), but as long as I don't have symptoms, I don't care.
Anyway, it might be coincidence that I am doing so well, because I only take 6-MP for a short while and it is said, it needs around 3 months to reach its full effect. However, I was always lucky in the past that drugs kicked in way sooner for me than for others.
I have no longer side effects from the 6-MP. The first three weeks, I had a daily headache (bearable, but annoying), slight nausea and spells of sleepiness that were beyond compare. It all had subsided. If it keeps going on like that and 6-MP is really to blame for my well-being, I don't care whether I will lose my hair etc. like quite some people have it after taking it for a longer time. It is so worth it for me - a million times better than suffering through flares and I have this stupid disease for a long long time.
Just make sure that you have your blood taken regularly and that you show up for your blood tests religiously. I went weekly in the first month, now biweekly for January and then once a month unless something suspicious comes up and needs to be tested.