I think I would be careful about how I used mechanical fasteners. If you only want an occasional pull out or if trying to decide about pull outs they will work fine. If they are going to be used a lot in the same place on the tarp I would be worried about wear in the fabric. It is not hard to use a backer patch and tape loop sewn on as a permanent answer. That can be seam sealed. YMMV, HYOH, free advice worth every penny paid. ;-)
I have side pull outs on my tarp and have decided that they do their job alright for giving me extra space in rain, but are a not good enough for high wind (maybe I haven't used them quite right...not sure how I could mess them up). I'm working on modifying my tarp to SGT Rock's pole mod. If you carry hiking poles, this works very well. I tested it last night as best I could without the full mod.