Builders in Quebec use felt under the buttons to keep the buttons from clacking when they bottom out. Now that does not mean that they always buttom out the buttons when playing. Most builders in fact use a smaller button so that when you press the button down your finger stops on the keyboard face plate instead of going all the way down. They also play very fast. So it boils down to what your preference is. I doubt either set up makes you play faster. You just need experience.

I just picked up my box last night after somewhat of a hiatus (aside from a jam last weekend). I noticed that my buttons go down in the holes, and I end up nipping my fingertips at times, which is somewhat uncomfortable.

I decided to do some surgery on my box, though not drastic. I took the keyboard edge piece off, looked at the leeway I had, and went looking for a soft shim somewhere in my house. I had some velcro lying around and used that, at first the two sides of the velcro stuck together.

I tried playing this, but it kept the keys up too high. I needed a little more indentation to keep my place on the keyboard. Next I just used one side of the velcro, and this seems to work.

No clacking either.

To me the felt under the keys is for comfort and noise reduction and in no way limits the response of the reeds or the playability of the box, quite the opposite in fact. The speed the reeds respond to the air flow is down to a combination of factors.

The gap between the reed and the plate. The smaller this gap the less air is required to move the reed so top quality hand made reeds will sound earlier (and clearer) than lower quality Tipo-a-mano or machine made reeds. (However the gap can be too small)

The size of the reed. The larger the reed the more air is required to move it especially the lowest 16' reeds but the better the quality box the less marked this is.

Overall condition of the box and build quality. Leaky bellows, gaskets, valves will all waste air and slow down the response of the reeds.

Basically, you can tell the quality of the box by the response of the reeds. If they all sound well, at consistent air pressures (both low and high), then you've got a good box