This is a highly individual setting. In my case the mic level is much lower, about 20 nowadays.
When I got my DYC-817 I tried it out in the shack first, and set the 817 to show the ALC. When I spoke into the mic the ALC indication was enormous! I switched out the compressor and tried it again and the indication was still far too high. ALC is one of those things you set and forget, it seems that something had changed since I got the rig - which I have had for over ten years. Either the mic, the speech amp or my voice had changed. I had to turn the mic gain down from 40 to 20 to get the proper ALC indication. There is no doubt that in recent years I had been overmodulating the rig, up to a certain point that is not too bad as running with the ALC a little high can simulate using a speech compressor, too high and your signal becomes antisocial, even at QRP! Anyway, to cut to the chase, I found no feedback problems.
One other point: on the Sotabeams site it mentions that the DYC-817 can be used with the FT-857. In fact the FT-857 already has an effective speech processor built into it, it is another of those “set and forget” facilities. I shudder to think what would happen if somebody tried the DYC-817 in their 857 without disabling the internal compressor, but in any case there would be no point as I tried comparing the two and there was no benefit in using the DYC-817 instead of the internal compressor. Mine will stay permanently on the 817.