I own both makes.
IMO both a very well made and I prefer them both over the Harris I owned and recently sold.
The GG&G is available in two versions, the standard one, which I own, and the heavy duty one, which is basically the same design, only beefed up a bit. I have used mine on an AR and a Savage 10BA without any issues. If I were to buy one for a heavier rifle, I would opt for the HD unit.
As mentioned above, the Atlas is probably one of the best 'regular guy/shooter' bipods I've used/seen.
But again as mentioned, they are very difficult to find these days as Atlas stopped civilian sales recently late last year for an unannounced period!
They do come up for sale once in a while on the EE, that's where I got mine. I noticed that you are from NZ, you may have better luck finding one out your way.
Another option, and this may be a real looooonnnnggg shot! But PGW (a vendor on here) offer their rifles with Atlas bipods. As they sell to the Military and LEO guys, they will still be getting a supply of bipods from Atlas. If you email Ross, and beg him a lot, you never know, he may sell you one. Again, this is just me "thinking outside the box", he may tell you he'll gladly sell you one if you buy one of his super sweet rifles!! ;-)
Good luck.
PM me if you have any other questions.