This is a cartridge developed for two very specific reasons. The main reason is that it fits in the "revolver-cartridge carbine and large-bore ex-blackpowder lever action cartridge" regulations established by some states that formerly prohibited deer hunting with anything except shotguns. With modern rifled-barreled "shotguns" generally shooting saboted 240-260 grain .44 or .45 caliber bullets at ~2000 fps, people shooting those same bullets at similar speeds from .44 Magnum and .454 Casull carbines wondered why they were not allowed to use their carbine. They eventually won that argument and in some states (not Iowa) rules were developed that allowed cartridges that were dimensionally similar to those cartridges to be used. The second is that the round is yet another larger-caliber round to try to make the extra-short action, moderate-pressure AR-15 into a sporting rifle since the standard .223 Remington chambering isn't all that great on game larger than a coyote.
The .350 Legend is essentially the equal of the .357 Maximum out of a rifle, but notably harder to reload as it is a headspace-on-the-mouth rimless cartridge. It performs a smidge better than the old .351 WSL cartridge (about 200 fps faster with 180 grain bullets) but about as much less than the .35 Remington loaded to SAAMI specs (~200 fps faster with a 180 grain bullet.) Generally the .35 Remington is used with 200 grain bullets (at 2100 fps) which are available but a reloader-only proposition for a 0.357" cartridge such as SAAMI calls the .350 Legend, but they aren't going to go 2100 fps in the .350 Legend since that's what the 180 grain bullets do.
I'd personally pass on this. If I wanted to shoot a .35, there are a number of much more suitable cartridges. You can go to most gun shops and buy a Marlin 336 in .35 Remington or order a Browning BLR in .358 Winchester or a Remington 7600 in .35 Whelen. Those are stock items and you'll get one within a week if not walk out with it that day as long as you are not in a goofy state with "waiting periods." You can also get a short-action magnum rifle rebarreled for .350 Remington Magnum, a short-action standard rifle rebarreled for .35 Remington or .358 Winchester, or a long-action rifle rebarreled for .35 Whelen by many gunsmiths. 0.358" diameter bullets are not as common as 158 grain 0.357" revolver bullets but are not rare, you can get them from several vendors in 180-250 grain weights in both jacketed and lead versions.
In a separate comment, I think the .35s are underappreciated. But, one can see why as they really only are "needed" to shoot moose and grizzly bears, game that is better hunted with rifles larger than .30 caliber. The largest game most will hunt are deer, which a typical .30-06 that most people can shoot reasonably well is far more than enough gun to cleanly kill elk, let alone a much smaller deer. Most will also think if a .30-06 will easily kill a deer or elk, why put up with the shorter range of the .358 Winchester for the same amount of recoil? Moose and grizzly bears would be good game for a .35 Whelen but the .338 Win Mag and .375 H&H are more popular and thus steal its thunder.