I've tried several different products. So far I like Safer 3 in 1 the best. I wouldn't say it is absolutely necessary, but it is certainly worth the effort and the few extra dollars. I think I paid like $8 for it at the hardware store and got two years out of a bottle. Still have a little left actually. It's OMRI certified so I'm not really losing much sleep over using it. I stop using it in the last 2-3 weeks of flowering, but by then the bugs aren't nearly as bad anyway. Some guys have problems with caterpillars and budworms late in flower but I never had any issues with either of them.
If you do decide to use it, try not to spray them in direct sunlight. Never actually caused any apparent damage, but it did give the fan leaves this weird plastic look. Also, it washed away fairly easily so it's something you'll want to keep up on to get the full benefit. I generally start spraying immediately after taking them out to try to avoid serious issues before they can start.
