Turns out if you make Heavy Storm Troopers and HK Assassin Droids with shorter range but cheaper, they're really really strong.
We're half way though our first Heart of the Empire campaign and dear god Riot Troopers suck to play against. I'm finding that there is little point killing one unless I can kill both because otherwise at 2 points to reinforce they're far and away the most cost effective unit. And killing two with starter weapons or even tier 1 weapons usually means a lot of attacks spent.
The Sentry droids aren't quite so bad, but they are better than probe droids and they may even edge out storm troopers. However they're certainly strong and the 5 health means you won't be getting "free" kills with blasts, cleaves and pings like you can with the typical 3 health units.