I'm currently doing the 300 swings a day for 30 days challenge. I did 10 days at 24kgs, best time 12:09, 10 days at 28kg, best time 13:54 and I'm 2 days into 32kgs, took me 18:19 this morning, looking to get this to around the 15min mark. On the last day I'll drop back to 24kg and see if I can get it under 10mins.
It was fun at the start but it's messed up my regular training now and I'm looking forward to it being over with. I'll do my normal training first, some lifting, some fast exercising and then the swings as a finisher. Overall I'd say it has negatively affected my strength, all my numbers are down.
There is a good article on breakingmuscle regarding Russian vs American swings that I thought was good.