it is worth every MP you invest in early game. it is macro depend to keep it safe. let it stay behind your VGs during combat, it works as LMG and no MP bleed as long as it is alive.. also it is great at caping non key points at start and FU and MU points. 15% faster caping and fast speed is key in early map control, the more area you have to slight advantage in resource income you will have.
as AchtAchter states I found good way to use kubel is not rush to FU to fight at FU point immediately but instead cap other points then go to FU when fight break out. use it to move behind HMG team that is combat your sqs and I result wipe quite alot of them if they think they can tank the kubel damage first to fight infantry, take the vickers (maxim will get away as it have too many men ) from my opponent for own use.
Totally agree with Appleseed. I actually get 2 kubels which allows me extreme capping dominance. Their firepower is not that great but together they are capable of chewing up an MG that is pinning your volks.
Back when I played USF I learned how great it was to be able to have vehicles do the fighting and repair the damage for free whereas a squad would need to pay to be reinforced. As a result, my kubels do most of the early game fighting and my sturms stay safe, repair and only fight when they can enter the firefight without being fired on much. The manpower you save this way will most likely be more than the total cost of the kubels, making them totally worth it.