I'm happy with both commanders. Lend Lease is a great addition for T4 play, giving both a HT and an all round tank to fill the gaps. The German one feels overall less focused on supporting any special tier, yet the puma works great on certain maps. It's mobility and range are it's strength. Command tank and Osttruppen Call-In are meh in my opinion - not good, but also not bad. Panzer Tactician is useful, especially with the new tank combat and counterattack tactics works nicely in combination with the Osttruppen. Their low upkeep makes them (sometimes) quite useful
If you wonder why these units - Western Fronts expansion is coming and probably contains those new units. Creating new commanders when all the abilities already exist is probably rather cheap and helps to 'hype' and 'advertise' the expansion. Relic gains advertisement by offering a glimpse of new units, community gains two new commanders, everybody wins. Except certain people here who always complain.
