Don't think Ive ever managed to make much use of Relief Ostruppen because I always try to preserve squads; particularly at 6CP its hoped they all have decent vet. For my two-penneth, call-in Ostruppen reserves would be much more useful.
You don't have to lose the squad, just the models. It's niche but it's pretty handy if the enemy is arty happy since it gives you infantry that can hopefully survive without a wipe but also cheap crews for your weapon teams.
I certainly like the idea of the ability but it's a bit pricey.
Could try halving the cost and only grant max 1 squad to make it more accessible.