4Game

It was an easy and kinda fun event, with a nice reward (a free tier 7!) without grinding 8 hours per day for 10 days (actually by playing each tank once per day, I managed to get the tank today)

BUT

my main concern is that it has no repeatability once you get the tank.
Since the keys are pretty much useless. If you could buy the camo with gold AND keys, then you'd have an incentive to keep on playing. Paying 10 keys for a single decal (I'd like to complain separately here that if you use a preset camo, you can't add decals and emblems, which kinda defeats their purpose) is not worth the time and effort of ~2 matches.

Now, that you don't even get xp, and the credits are too few to grind like this, once you have the tank you stop playing. That means that as the event reaches its end, even fewer people will play it.