Gerard,
The nominal resolution of the MiniSGH is around 0.2A - the equivalent of a double stacked etalon (Lunt or Coronado) PLUS AN ADDITIONAL ETALON!!!!
Basically a "triple stacked" performance.
The bandwidth is centralised on Ha so there's no "leakage" into the wings.
With the Upgrade I'm looking at (New 125mm FL lenses and a 10 micron slit plate) the resolution should improve to 0.13A
No commercial solar filter I know off reaches that resolution.
Unfortunately seeing conditions will impact on the outcome...
.
Onward and Upwards.