The saw is a Makita, blades 4 1/2" to 5".
Personally, I have re-done many teak decks this way and so has my trained crew, without any tool slips.
I have and find the Fein MM to be of limited use for professional work and prefer various stock and custom hand tools faster and better suited.
The small circular saw with stacked blades and with a guide pin set at the rear of the saw when operating is by far the fastest and easiest method remove the old deck caulk, deepen and clean the seams for new caulk I have found.
Be sure to run the saw backwards so as to keep the work area in...