I have both Atlas and Harris. I like both, hard to say which I like "better".
My Atlas is 6 inch to 9 inch, but I got extra 3 inch extenders for it, so that put it into the 9 inch to 12 inch space.
My Harris is 13 inch to 27 inch, so it is in a different space. I can shoot prone at 13 inches, sitting at 20 inches and kneeing at 27 inches. In rougher terrain I need this elevation up off the ground.
So for me, the Atlas is my "low" bipod and the Harris is my "high bipod" but that makes them difficult to compare directly.
The Atlas can get lower, because you can flair forward (or rearward) the bipod legs, the Harris cannot do that. The intial cost of getting them usable was about the same, $220 for the Atlas and $110 for the Harris + $66 for the rail mounting system. However, the 3 inch extenders added another $50 to the Atlas cost.
Probably the most significant difference between my Atlas and my Harris is that the Atlas will "pan" and the Harris will not. You can "twist" the Harris but you are putting pressure on the legs and have to hold it, whereas "pan" on the Atlas works the same as "cant" does on both. You "pan" the Atlas and it holds for you.
I also like the Atlas ability to acheive intermediate positions with the legs. The Harris takes a bit longer as you have to use the pressure screws, but the Harris allows more variation/precision in adjustment.
The American Defense QD mounting for the Harris is so easy to use, it is truly "tool-less" to remove it and mount it on a different rifle. The Atlas requires a screw driver to move. Not a huge plus, but I am reaching for differences

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Another advantage is that I'd be more comfortable mounting the Harris on ANY other rifle because it has a solid sling mount system (the default for Harris). Any rifle without a rail, cannot take an Atlas without another part. P.S. Atlas makes a rail converter for the Savage 110BA, so I got one of those! They make the parts I need!
I like them both, if I had it to do over again I would get both. They both are great

. If you mostly shoot prone or low to the ground, maybe I'd go with the Atlas as it might occupy less space overall in a minimal configuration. But if you ever need to shoot higher off the ground, the long legged Harris is the way to go.
If I had to get another bipod today, I would probably get a Harris. Newer Harris's have real "pan" and I think they are more flexible to mount on rifles without rails. And they are cheaper. If I was going to use the bipod primarily on a patrol/light precision rifle, I might get the Atlas, because I think has a smaller 3-D footprint.
If I bought an Altas I would buy it directly from BT in Kansas (I'm from Kansas)

!!!
BTW, my rifles are:
Savage .338LM
Sig716 7.62 NATO
Mossberg 715T .22LR
And I use both bipods on all three rifles. I also have a UTG "training bipod" I got for $60, it usually sits on the third rifle, the one I am least likely to shoot this week, but is technically designated for the .22LR (my training rifle). It is similar to the Harris but has no "cant", so I have to adjust the legs with the pressure screws to get level. This is the biggest downside of the UTG.