The striations are filled in a bit by spray primer. They are still there, but you have to hold at an angle to the light to see them. I'm going to finish painting the bolter I have now and see how much the paint is capable of filling. Liquid green stuff is also an option, but I've never used it before so I can't really give any advice on that. I'm considering picking up a pot to review on my blog.
While FUD is a bit brittle, the bolters did not break when I put stress on them. It does take more pressure to break the FUD sprue than the normal GW sprues, but FUD is not soft like GW plastic either. I feel that close combat weapons (if made properly) won't be any more delicate than the stock GW fare.
Here is the WIP of a Dark Angel thunder hammer I've been working on:
As long as the parts are firmly anchored and have a good length to thickness ratio, you should be fine.
I just got a driod bionic, which seems to take way better pictures than my camera, so I'm going to try to build a photo box and get some good, HD photos of everything.