Given your whole idea (its dmg, range, delay) this ability would only be dangerous vs emplacements. In 30 sec (even 15) a good player can move all their troops. And paying 400 ammo for a couple of emplacements is... not that good trade.
Both Puma and StuG have superior range. Just micro them and they will be fine. Watch out for AT guns, don't chase him, try to make your enemy rush after your squads and set up traps.
Since we are here and I find making new topic irrelevant, could someone tell me when to buy lmg and when to buy stg44 (from specops doc) when it comes to upgrading Obers?
Two things that came to my mind when I was reading your post
1) Have you tried using control groups? Doing so will allow you to quickly look at what they are doing, just by double-tapping group number.
2) Try looking at the minimap as often as you can (like every couple of seconds). Checking a tactical map is also a very good idea to help you keep your awareness on what is going on.