I like Simmons as a lock. Sure he's not as flashy and as noticeable as Pyle, but he is excellent in the line out, makes plenty of tackles, hits rucks (would like to see him doing it more effectively than last weekend though), pushes in the scrum and has a good work rate.
I wouldn't be inclined to have him in a fully fit back row ever though. The Italy game was a good option based on available players, and the opponent. That would really not apply in this case. If we were playing the Stormers and it was part of a reshuffle and one of our first choice line out jumping back rowers was injured perhaps. But if you are talking about making those sort of changes, you should be going for Beau over Gill first before you start looking at playing blokes out of position.