I suggest against using them. Yes, they do remove a lot of crap most of the time, but most of what comes out is harmless deposits. The real problem that can occur is not what comes out, but what stays behind. There will be trace of the flush in the fresh oil, but the worst thing is that the flush may not remove all the deposits, just loosen them. The fresh oil goes in after flushing and the engines run for a while, the deposits that are loose may then break free, meaning there are hard bits in the oil. Not really what you want.

Cheers

Tim