Phil Mickelson (famous for experimenting with equipment) tries new clubs with goggles on. He doesn't want to be influenced by the ball flight. He has spotters (Dave Pelz being the most famous) watch each shot with a new club, while he tells them if it was a good swing or not. That way, they can come up with tendencies without him being influenced by seeing the ball flight, which he would adjust his swing for.

If he can't do that, Mickelson hits one shot with a club, then switches to one of his existing clubs, then back. That way he can figure out how he's swinging that day. If his 5-iron is going straight but a new club (say a hybrid) is hooking, then it probably needs tweaking.

Mickeslson also likes to look at video tape of when he's swinging good as a reference point, arguing that most amateurs should also be filming themselves when playing well, not just when taking a lesson because they are playing poorly.

If you like equipment, you'll enjoy this Podcast. Give it a listen!