They're all the same light and all probably made by the same manufacturer. The original distributor was Mcculloch and called the X990. About a year after that a few Maxtell's were bouncing around the market and then for the last couple of years it's been sold under the name Acro and called both the X990 and 990X. Today they're sold with black painted swivel heads but some of the early Acro's were still chrome heads like all the Mcculloch's and Maxtell's. During one discussion with Rob at Magnalight, he refered to Acro as the mother company and maybe that is indeed the case. I haven't researched it though and have no idea if Acro is an actual manufacturer or just another company who is putting their name on the light. In any case there really isn't any variation in these lights other than the black or chrome head.
It sure is a great light other than the expensive batteries. I'd have to say that the N30 is a better light overall and with the L35 coming out it would be hard for me to every recommend the X990 at full retail. The one which you saw sell in the market place was a great deal.