The Raptor and Owens are the only two that can hit +4 (at least with out IJJ, which could be used to give the Blackhawk or Strider that ability, if you were strange) so they can work as fast lights. The existance of the Raptor F is a huge boost for it, of course, but many of the others are servicable. Its a bit frail, but its 25 tons, so its bound to be a bit frail, and for me it lasts pretty well. It reminds me a lot of the Fire Falcon, which I adore, and that's part of the draw.
As for the Dragon Roars, all the Combine's omnis got a veriant with mostly Clan tech (some got more mixed, some got the full Clan treatment). They now exist as "R" veriants for each. Some are really excelent (the Raptor looks like a Fire Falcon B, with ER LLs and a TC) some are mixed (the Avatar gets a Clan GR and ER LL, but also an IS MRM40, which is cool if you like big damage, but not so great if you like accuracy) and some are still useless (the Owens gets three Clan ER MLs, which is always a good start unless you've got single heatsinks, and blows the rest of the tonnage on a MRM10 #P ). They came from opperation Bulldog salvage, and I belive to be semi-common in units with high Clan and omni ratings.
One of the things that they and other new veriants are good for is really milking the omni advantage to make up for a key weekness of the first generation of IS omnis: antiquated configurations. While 3058 saw a giant leap in design philosophy that saw the outbreak of twin gauss monsters, it didn't see any new tech, and so as a resualt the 3058 omni class tends to have pretty low tech configurations. The Sunder Prime uses all level 1 guns, and key configurations in all the omnis are saddled with older tech weapons. No ER MLs, no big Ultras or LBs, no RACs or TCs or stealth or any of the really fun stuff. So some of the best veriants tend to be new ones, like the Avatar F, which is basicly a retred of the Avatar A, but with an LB20 in place of the old AC20, or the Raptor F, with its 7 jumpjets and 5 ER MLs.