I’ve had two VSTs for many years, and have enjoyed them. They perform as advertised. I’m not home at the moment, but believe I have the 18 and 21 g versions. I use a bottomless rancilio PF and they work fine in there. I’m confident that the diameter will fit your Brewtus PF, but it’s possible that the depth won’t work. For example, they don’t fit the two-spout PF on my current ECM E61 Synkronika because the PF bottom slopes inwards and there is interference.
Happy to check on this with my old Brewtus when I’m back home Saturday if you’d like. Please remind me.
Also, the tamper from VST is spendy, but I feel it’s worth it—it’s of course perfectly fitted to the baskets.
best,