... what will be the differentiating factor between say the Lee Auto drum and the Rcbs uniflow or one of the Lyman options on the market
For pistol, no difference.
All powder measures work exactly the same - they contain a cavity that fills with powder, which gets dispensed.
The difference between measures is the amount of powder they can dispense, and the mechanism they employ to dispense.
Some are case activated, others are manual.
Going back to your question, there are pistol powder measures and rifle powder measures.
The Lyman measure is a rifle measure, It is very difficult to adjust it down for pistol powder volumes, and make incremental changes.
The RCBS uniflow is one I've never owned, just make sure the rotor is for pistol, not rifle.
The old Lee auto disk is all you need for pistol reloading. Get an adjustable charge bar for it, and it's as good as anything on the market, with the added benefit of it being case activated.
Either that, or the newer model.
If you want to spend more money on it, the Hornady powder measure with pistol rotor and case activated linkage is excellent.