I'd be pretty reluctant to make the ability any better but the idea of making it free to give it more incentive to use has some merit. Will look into that.
Yeah if it's gonna nerf the biggest tank you have on the field then it should definitely be free. It's downside should be the performance nerf, and if needed that could even be tweaked to make it more/less powerful instead of adding a cost.
I really don't think OKW should have access to teller mines though. People tend to always say tellers are necessary for ost because they don't have good light vehicle counters, but this doctrine already has a 5 man double schreck squad and puma is still a thing. Tellers are already incredibly frustrating and they'd be even more so if you put them in OKW, who don't
really need them. I'd be fine with like some sort of mine that only vehicles can hit if it doesn't one-hit lights. It's honestly a BS mechanic that goes against what coh is supposed to be the same way snipers and the old demo charges (which got nerfed) do/did. It's either you happen to stumble across it with a sweeper and you defuse it or you don't and you lose your vehicle to a single hit. That goes for M20 mine too btw.