I still have a hard pre 2005 Pro D Magnet in the bag since 2006, was my brothers he tried for a single month with bit of putting work in the back yard and with putting a round about 1 to 2 times a week, so the disc was just broken in. It was then stopped as he did not like how much glide the disc had. The other 2 putters in August 2018 that are just putting are Jawbreaker Magnets one beat more and labeled Approach for long putting and hazard putting, the other labeled Putter for putting, both I copied the ring from the stamp on both, thumb placement. All Magnets are 173-174 though the old hard pre 2005 disc feels like it is 170 grams +/- 1. I had a 2006 softer hard Pro D Magnet in the bag but the disc hit a tree in late July and could not be fixed even with weights 2 20 LB on top of the disc for 5 days. I threw the disc in the Recycle. The 2006 softer hard Pro D Magnet was starting to feel like a soft Pro D Magnet that is bran new in terms of the softness, no other factor so I needed to get new Magnets and was looking at the Jawbreaker but they did not have the Ring Stamp to help me with thumb placement.
Sorry long post but it shows that I keep the disc in as long as it feels right in my hands. The pre 2005 hard Pro D Magnet might stay in my bag until the disc breaks though and I have to find the stiff Legacy Clutch in Protege plastic. Not that it should, I rarely use that old Magnet anyhow.