Although they both will work just fine in most applications, IMHO it's really just a trade-off between cost and functionality.
On the Safeair mount, the entire assembly (mast and baseplate) is welded together and attached to the main spar flange and bottom wing skin as an assembly.
On the Gretz mount, the baseplate and mast are separate assemblies - the baseplate is permanently riveted to the spar flange, bottom wing skin and to the wing rib, and the mast attaches to the baseplate with counter sunk screws into platenuts installed on the baseplate and is entirely removeable.
The baseplate on the Safeair mount is slightly smaller than the Gretz, but I assume you could use an aluminum angle to attach it the rib as well as the wing skin and spar flange (similar to the Gretz) to make the assmbly more rigid and prevent potential skin cracks due to vibration.
I installed the Gretz, because I like the ability to remove the mast with the baseplate installed permanently. It makes storage of the wings a little easier until the wings get mated with the fuse (without the mast sticking out and getting in the way), and because the Gretz is a little heftier with the larger baseplate and thus more rigid. Also, I think it may make it a little easier to install and remove the pitot tube as well since you can move the mast during assembly/dissassembly. I did still notice a little bit a flex in the bottom wing skin even with the baseplate attached to the rib, skin and spar flange, so I added a skin stiffener (similar to those in the bottom fuel tank skin) between the ribs in the bay that I mounted the pitot mount. With the stiffener installed the entire assembly is very solid.
On the other hand, I believe the Gretz is a little heavier.
Like I said, it's a tradeoff and thus personal choice.
