I have a Fein, and use it quite a bit. As an example, when taking a cabin trunk up off a deck to slide the new deck covering fabric under the trunk, it was necessary to loosen a lot of bolts, and then remove 50 #24 X 4 bronze wood screws that went up through the deck into the side of the trunk. Maybe fifteen of those broke off, or the heads were too buggered to back out. Instead of spending maybe an hour on each of those screws drilling them out, I used the Fein saw to slide between the deck and the bottom of the trunk's side, and cut the screw off. Simple. Quick. No damage.
For reefing out glued seams it's quite good. For sanding up to edges.
But mainly for flush cutting with almost no kerf.