Flames fan here:
With Sieloff, you get a prospect that is a bit behind due to his injuries (he could have died at one point, IIRC, from a staph infection).
At any rate, he has had a couple cups of coffee at the NHL level, and looked better than I thought he would. I thought he actually looked better in the NHL than he normally does at the AHL level. There is some NHL-potential there.
He skates well, he will fight, but he isn't the biggest body. Defensively responsible, hard and accurate shot, but doesn't score much (weird, I know). He makes a good first pass, and skates well with the puck. You watch him play and you think "hard hitting puck mover", but he doesn't get on the score sheet much.
I wouldn't write him off. He was rather buried in the AHL in Calgary (was actually surprised to see him brought back up, but probably had to do with his strong training camp/preseason), and would have even been buried deeper this year with a few kids turning pro. No idea what your system is like, but if you guys aren't too deep in defence, I would bet he turns his game around and becomes a solid depth defencemen who can be trusted defensively, and who can make the occasional devastating hit on an unsuspecting forward.
FWIW, fans definitely understand why the deal has happened, but I don't think anyone is happy to see him go, other than being happy for him in getting a chance to get his career back on track. Solid character guy, with NHL upside.