I had Devi stuff (DeviMat) fitted in my bathroom, works well but I’d avoid the DeviReg Smart controller if I were you (I couldn’t get it working at least and I’ve worked in IT for 25 years :p lots of complaints about it on forums when I started digging). I have the DeviReg Touch controller and it works well (the Opti looks interesting to but wasn’t available when I had mine fitted), you rarely need to mess with it so I don’t mind not being able to use an app on my phone to control it.
I actually wanted Schluter Ditra stuff as it seemed a bit more thought had gone into it but my plumber couldn’t get it under his trade discount so it would have worked out a lot more expensive.
I have DeviMat on one wall to (instead of a towel radiator), works really well as the towels create a hot spot behind them (45-50c) which dries them well. It does mean a second controller though.
Oh and in winter it’s expensive – about £70-80 a month I was finding as to actually heat up the room you need it on a lot (I had it come on at 1am for me to have comfortable temp at 6am, even then the room wasn’t actually warm). I’ve had the floor switched off completely since June and when it’s about 10-15c outside temps I found just having it come on a couple of hours before I used the bathroom in the morning was fine as it was mostly just taking the cold out of the floor tiles.