Is there a difference in perception between a UK and a US Masters?
I'll note that the UK masters degree starts (in mathematics at least, and probably other fields) starts with a deeper base, since the undergraduate degree in UK is much more specialized and focused than that in the US. So, it is possible to go farther, since you start farther along. This also explains why there is usually more research done in a UK masters than might be done in a typical (but not exceptional) US masters. 

But the perception would depend on people knowing that. Some will and some will not. For academic advancement, I suspect that doctoral admissions systems understand it well. In the workplace probably not so much. 

But seven years out, in industry, your best credential is yourself and your own work.