I have been using both for years and they can work together depending on how you organise your workflow.
FormZ is much faster for roughing out a concept but SharkCAD has a deeper toolset for product and mechanical design.
Coming from Shark LT I don't think you will struggle with FormZ it is much more direct and easier to understand.
It is better not to look for feature parity though.
Kind of interesting is that Vellum Cobalt has reappeared at a lower price point and is being sold alongside Strata3D products as well as on the Ashlar-Vellum site.
Almost identical to SharkCAD but Cobalt still has the constraint system that SharkCAD was forced to drop after version 8.