I also have a 2 speed pump (2.5 hp) that runs on low for 95% of the time. My pool sweep has a booster pump and this works fine on low. The heat pump usually does not have a problem on low speed but when the pump basket is getting filled with dog hair it sometimes won't start. The flow through my system on low is noticeable and the skimmers work fine.
For the person who has problems with the heat pump not running on low you can sometimes adjust the pressure switch in the heat pump or downsize the return eyeball size just a bit in one eyeball to create a little more back pressure.