Specter is the top of Topo's road line and the 3 is a full redesign rather than a refresh: a new RevFoam ATPU midsole and a reworked rocker for a quicker toe-off. The heel is 39 mm, but the low Topo drop and the wide toe box mean it does not run like a soft, tall shoe.
It suits you if you want one trainer covering the easy days, the long run and the weekly up-tempo session, and if Topo's foot-shaped fit is why you buy Topo at all. Topo itself files it as up-tempo training.
It is not a race shoe. There is no plate in it, so at marathon pace it will not do the work for you, and Topo makes lighter shoes for a track session. Nor is it a low-drop conversion project — coming off a conventional road trainer, build into it over weeks.