Generally engine flushes are a bad idea, they tend to loosen oil & gunk buildups and put them into the oil pan, but since most pants are baffled they dont drain easily, and tend to get sucked into the oil pickup. It's not unheard of to clog your oil pickup tube after an engine "flush". Only way i would even consider doing one is if i were going to also remove the oil pan after the flush.

ATF does work a little but makes a very minimal difference since ATF and most engine oils both contain detergents. Its more of an old shade-tree mechanic myth.