I found that it's a YMMV thing.
I've never had a problem getting paint to stick to the things. Granted, I often run a quick soap-and-water wash on them to get the mold release residue off (put in container, put dish soap and water in, put lid on, shake like it's going out of style) and I've said my fair share of rude commentary about stuff that /does not want to stay put/ - some models function better in metal, frankly - but overall? I like that they're practically indestructible, light weight and detailed.
I do find that Reaper's paints stick to them best (apparently, they really /are/ formulated to bond to these things), but I use whatever I have handy, from Reaper's MSP to P3 to Liquitex, and ... yah. No problem. YMMV.
If you want minis you can give to the kids, let them paint them, abuse them, whatever, these are probably what you want. If you like the feel of metal, these are going to be flimsy. If you want something to show off ... um.. buy those aggravating resin things.
Beorn, a lot of the minis I've been showing off in the other thread have been Bones. Including that Marilith. *shrug*