They were only available at TRU during the holiday season (TRU probably had some kind of exclusivity deal before they went belly up) and they seemed pretty popular. The dolls recently started appearing at Walmart after all this time.
I have seen the larger dolls at one of my Walmarts.. and I was not impress. Some more minis did start to pop up after I haven't seen them for a while... oddly it was some of the Rainbow Rocks Minis oO Which should tell you something about my stores
I never saw them at TRU in the UK but they have been at Smyths and in Morrisons. I think you are right that they are trying to snatch MH people. Interestingly enough I often find them at carboot sales in bundles of dolls with MH dolls as well. I think probably it's exactly the same target audience and a lot of kids had both together. It makes sense for Hasbro to think they can now own that space...although I'm not sure they can.
Morrisons are ridiculously expensive with these dolls as well. Especially knowing they cost $10 in the US, to charge £15 is stupid (rrp in the UK is already bad enough at £13.99). I wonder if that is putting people off.
I have the new Sunset Shimmer and I like her but she has to live with the MH dolls, she doesn't fit in with my EQG dolls and I like the old goofy ones better. I don't know how well they are selling, but they do seem to need to restock from time to time in Smyths, so maybe that's a good sign.
Lots of Minis on clearance here at the moment...the sets with Shining Armour and with Adagio.