I've been half tempted to have a go at one, but it's hard to think of too many situations where it would be of use commercially. A 200T isn't really all that heavy, climb with it every day and it's an extension of your hand. I don't notice mine is there. It's a circular argument; yeah it needs less energy to use the smaller saw, but then you'll get weaker from it too won't you? Add to that, unless it's just light pruning you're going to need to change up to a bigger saw earlier. The smaller saw reduces your cutting options also. People make the point that some of the lighter/less powerful saws are only fractions of a second slower and that it's therefore not worth getting a more expensive/more powerful saw ie. in the past a 200T. The real truth though, is that branches aren't just going to hang about while you are cutting. They're going to start folding! Those fractions of a second make all the difference in controlling the attitude of the piece as it leaves the tree, which then in turn makes the difference between being able to free drop it vs having to rig it because you don't have the speed to spear it or pop it off. Once you've had to start roping more stuff, the time gets massively increased, so the saw that was only fractions of a second faster comes out hours ahead. You really can't have enough power in a climbing saw in my opinion. Shortest bar you can get away with, most aggressively sharpened chain it will run, muff modded, tuned right out to the ragged edge... and a little more power would still be nice!
The 150 has it's place I'm sure. But it's not as a climbing saw. It is an ideal saw for amateur use or occasional homeowner light pruning work. You could get away with using it commercially as a light pruning only kind of saw, but that implies then that you would also have a real climbing saw for general use, and several other saws too. If it's a one saw plan for climbing, then it's not a 150.