[d__k]

It probably depends on the type of equipment they buy, that is, how complex it is and what are the maintenance costs.

For example, Turkey recently declared that they will buy some kind of Russian advanced anti-aircraft system so they probably think that it will be cheaper in long term than buying it from a NATO member. Yet, even in this case they had quite strong tensions with NATO and it is not clear if Germany wants to have (and can afford) similar tensions with NATO, even if these Russian helicopters are technically better.