The Mastia is a good all-round performance rock shoe with a varied focus, says Rob Greenwood, ranging from overhanging sport to bouldering on rock types which require that little bit of extra sensitivity.
As a long term Iati wearer I tried the Mastias and really like them. I'd concur in that you need to size them down a fair bit. For me I've tried a half and a full size down from my Iati, and they're still 'comfy'. I find aggressive shoes (like solutions, ninjas, instincts etc) excruciating and prefer comfort over absolute performance, but have found these Mastias to split the difference of being a very high-performing shoe, without the pain. I think the heel is great on them. They made all the difference on something like this boulder: https://www.youtube.com/watch?v=9JoQVjdV6D0&
You were looking super smooth on Electrical Storm too. I remember finding those first few moves the living end! The most memorable 'game-changer heel' move I've ever done was on Lay-By Arete (f7B+) at Slipstones, where it went from feeling absolutely impossible to unbelievably easy within the space of a single pair of shoes.
As for The Trench, I could have spent the whole video raving about how good it is
> When I did some of the problem in the Trench, I was thinking how is this 4+?!? I think I managed to just about wobble my way up one of the 5s, but that was it!
I feel the same way almost every time I go to Font. Penny and I often have a thing about doing the 'easy' circuits and trying to guess the grades. Usually if you guestimate what it is, then remove around three to four grades, you're right on the money