I'm a plumber 30 years experience used these for about 10 years they're great. If it leaks you've done it wrong. If you want to demount it, you don't know what you're doing.
I purchased a pair of these tees, mistakenly from the visual, believed these to be the tees from the Conex range (The Conex ones are removable) unfortunately I found out after filling the rad system one of the joints was not holding tight, but because this was the inferior Pegler one, you will have to use a Dremel and a fist full of cut off disc's to remove them.
Annoyed now as it's taken 45 mins, and 12 cut off disc's just to remove the old, this is also complete with a large hole in the wall I had to make in order to get the Dremel inside.
My advice is to use the better Conex ones because they (with a bit of a faff) can still be removed
