This is a timely thread for me. I'm finishing a GSM-1 at the moment. My first attempt was with Feast Watson Prooftint in mahogany with a black burst. This was after applying Ebony Timbermate, but no sanding sealer.
The timber took up the stain very unevenly, and it didn't look good, as much as I tried to like it. So I sanded it back, and this time applied sanding sealer before the stain. It's not exactly like for like, as I've decided to go with a natural black burst rather than mahogany. Here it is after the sealer was applied and sanded back.
And here it is after the black burst.
The sealer went on easily, and sanded back to a very smooth finish. It made applying the stain much easier and more consistent.