I have Maggies, and I have a love/hate relationship with them. The sweet spot is extremely small, it is a pita to position them, they are large and clumsy, but oh, the sound…
My amp is a Jeff Rowland Concentra II which is able to drive them without any problems.
I tried a BT20a Pro as a replacement for the Concentra, and while it performed quite well it was audibly worse than the Concentra.
I also tried the V3 Mono, and imho they are comparable to the Concentra. Their sound is a bit different than the Concentra, but the Concentra is a class A/B so this is to be expected.
But whether the difference between the BT20a Pro and the V3 Mono is audible in your system, is extremely dependent on your loudspeakers.
TLDR; Yes, the V3 Mono are definitely better than the BT20a Pro.
Cheers, Joe
PS: Why am I experimenting with other amps? The Concentra is 20 years old and one of my worries is that it might die one day. And for that day I want a replacement, which for me are the V3 Mono (for an unbeatable price)
PPS: I find it utterly fascinating that with modern DACs and amplifiers the cost for a „first-class“ system has gone down massively. The determining factor today is the cost for the loudspeakers, and I would say (gut feeling), that you should invest 70-90% of your overall budget into them.