Its all about the smoke mate....... they all run on smoke.... if you dont believe me, when you see smoke come out of an electrical component, i can bet it wont work anymore.....
To be honest I'm still not fully understanding the pros and cons of different R/R designs: SCR, Mosfet, Series. The conclusion from reading what I suspect to be wise peoples words is that the SH847 is expensive but will reduce load (heat) on the stator.