Scotty Cameron Long: Who are these new 38" putters for? 

You are using it incorrectly. The lie and especially loft on these putters are not set to be an armlock, youd be delofting it too much. These putters are strictly counterbalanced

I tried a lab putter, what I didn't like is the lack of feedback. I had no idea where on the face I was hitting and on long putts had distance control issues. Short putts felt good though

That video is coming soon. - DD

Maybe, but ideally you would hold these putters in the same way you would hold a traditional-length putter while allowing the extra length in the grip to go above your hands. You don't stand more upright using these putters. - DD

In the standard length Phantom 11 it’s 370g in the 33", 360g in the 34" and 350g in the 35", but the Long version has 25-gram weights instead of 10-gram in the traditional lengths.

I would not recommend doing that. Would the effect still be there? Yes, but extended-length putters are designed to be held like a regular putter so a portion is above your hands. Cutting the putter down reduces the effect. If you are someone is 5-foot-2 or shorter, I could see going with a shorter extended-length putter because it could be extremely unwieldy or awkward to use, but aside from that, I would not cut one down. - DD

You could, possibly, but you might need or want a flat-sided grip to make that technique more comfortable. - DD

No, probably not. Plus, Titleist is selling them at other extended lengths like 37”, 38.5”, etc. through custom order, so you should be able to get one with the ideal fit. - DD