Pros: Accurate, Fast, Small, Well Built
Cons: Just the fact that the face plate swap-ability doesn't make it legal :(
The GX-4 was released under the hopes that the bright yellow "faceplate" would make the device legal when the "silver" faceplate was on. The yellow version "enables" (likely via completing a circuit or something basic) the "slope measuring" capability of the GX-4.
Unfortunately, as the actual device still has the hardware to measure slope, Leupold failed in that regard to get by the rules.
So it's kind of tough to justify the added cost for an item you can't legally use in tournaments or sanctioned play, even those that allow distance measuring devices (DMDs).
But rules issues aside, the device works GREAT. It's small, heavy duty feeling, and fast. The battery lasts a LONG time, several thousand actuations, and it's as accurate as anything out there. The bright red display is super easy to read, and the device locks on to objects quickly and easily. It fits in cupholders, unlike some lasers, and is precise enough to target the lip of a bunker, the flag, the edge of a creek, the cart that may or may not be out of range, etc.