I use them. I have many different brands of mags. I carry a Springfield with a Metalform in it and a Wilson Combat mag as a back-up.
BTW, Springfield includes them with the Professional Model. That ought to tell you something.
I have Metalform 45-797W (7-round flush fit) with Round Follower and Wolff Spring for sale for $35/2 mags including shipping. Please let me know by PM if you are interested. I take payment by Paypal or Money Order.