I didn't realize it was Amsoil Engine Flush, I have no experience with that product, but it seems to be one of the best companies out there for high end oil products.
That being said the flushes that I have heard and seen seem to be really harsh solvents and are tough on the engine and its seals. Although you drain the engine soon after you flush, a little bit of the solvent stays in the engine compartment and can complicate the following oil change(s).
Yet again I dont know about Amsoil's product, but from what I understand Auto RX is much less harsh than engine flushes and there are more positive things to read on this board about it than there are most other products.
With all the Oil nerds hanging about that is high praise.
If anyone else has used Amsoil flush please correct me. It is interesting that such a reputible company would offer such a product when most Flushes are notorious for their harsh and toxic chemicals.