Slitherine

for the Russian aircraft before Smolensk?

Only if you're running denied airforce or something.

For collection, maybe. Russian aircrafts at this era is no match for your own, and you won't be able to use up all your cp even if you accept every exchange at this stage, if you can finish all secondary objectives.

i think it depends on your general traits
if you take slow modernisation (6 months later to get the new stuff), the units you get trough the exchange are more usefull instead without the trait,

thanks i passed but you never know. most Russian equiptment is welll worth it