"And as long as this guy isn't using it at a tournament (I think it's NOT regulation),"
I looked through the USGA rules on putter design and I don't see anything that would make the Gilmore putter illegal (the Odysee one, that is). You can look for yourself. Follow
this link, Scroll down in the column on the left until you get to Appendix II. Click on it and it covers all club design issues.
FWIW, My father-in-law used to use an old hickory shafted blade putter. He found the head at some thrift shop, sent it off and had it gold plated. I shafted it with a hickory shaft (can you even get those any more?). Shaped it and finished it and installed a leather wrap grip. He was deadly with it! People might laugh at first, but they won't laugh when they're giving you their money.
BT
EDIT:
I found some more recent revisions that might make the Oddysey version non-conforming, but I'd have to have teh actual specs to know. Here they are.
From USGA.org -
These new guidelines can be listed as follows and are illustrated in Figure 32:
(i) The distance from the heel to the toe of the putter head must not be greater than 7 inches (177.8 mm);
(ii) The distance from the heel to the toe of the putter face must be no less than 2/3 of the distance from the front to the back of the head;
(iii) The distance from the heel to the toe of the putter face must be no less than 1/2 the distance from the heel to the toe of the head;
(iv) The distance from the sole to the top of the putter head, including any features, must not be greater than 2.5 inches (63.5 mm).
Also, new rules state that if the putter is deemed to have 2 striking surfaces (front and back are both flat) they must be made of the same material and have teh same loft. So, the insert would have to go. If the back of the clubhead is not flat, then no problem.