Vests effectively counter phys mechs unless they have res drainers, 2/3 are L-Ms so hard to get and in lower ranks nobody even thinks of using them. This is a no.brainer if they already have it.
If you have a mobile device, install supermechs there and it should reset once you watch one ad there. This is a bug that happens if you deplete all the ads on desktop version, you always need to skip the last one if you want it to be there the next day.
Hard to do reliable data analysis on something that you only get one of per 3 days, I think the fact that they don't stack with regular fortune boxes means the droprates are at least somewhat different. Then again, might just be a bug seeing as there are bugs that haven't been fixed for years.
OD8 2v2 on hard is optimal, OD8 1v1 on insane if you can't beat the previous one consistently. If you only care about boxes and not about gold whatsoever one of the first boss levels that costs the least fuel is the best even if the droprate per level appears to be lower.