I have heard nothing but good reviews about all butters welders, and miller generally have a good reputation too. not sure about the britweld name though, haven't really heard anything about models with that name on
M8 I would get a butters. I weld everyday for a living on different thickness material and have had mine (271) butters for 6 years and its never let me down.
IIRC when they originally went bump they were taken over by Britweld which I believe?was part of the Parweld group.
The original NBC machines were very well built ,We used to put Butters rectifier stacks in various machines because they were such good quality.
After the take over they weren't the same but still better than most of the imports .