Which ones have you looked at? I designed one for jets in particular and have been flying it on several of my models.

http://www.hyperdynelabs.com/products_RC_stald.php

It includes the stall speed alarm feature as well as flameout detection (w/ extra circuit). Lots of options and all settings are programmable. Speeds are called out via earbud by number, not by a gradient tone. You use the eagle tree speed sensor with my unit, it simply plugs into the Tx board.