They are identical lenses. One with the makers trade name, geronar, and the other with the Calumet housebrand name, caltar. It's a good first lens but it will not get really sharp until about f16 and smaller. They're a good value for a beginner mostly because you're getting a first class shutter with it.
Be sure that the shutter operates flawless, also to slow times, they should not be sticky.
I have got too many lenses with inaccurate timings or whith only B and T settings operational. It's a real pain, even if the lenses are good.
There are at least two threads on this site about the Geronar, because I asked the same thing myself when I started with LF and the Geronar 210 came with the camera. You can read the posts if you like, but as I recall, they were pretty favorable. I use mine stopped down to at least f22 and find the results are sharp and contrasty. Unless you enlarge beyond 16x20, you'll be satisfied with the results I think and maybe even larger, but I haven't done so, so I can't comment.
The other option is 180 F5.6 FUJINON W COPAL BULB, TIME (4X5)(42 MOUNT) (58) WITH CAPS, LARGE FORMAT VIEW LENS which is another $100 more than what I planned for. And on KEH this is LN- condition.
Don't buy a lens for more money than you planned for. You are looking at a 180mm and not a 210mm (see your first post), even though I'd suggest you a 150mm or 180mm lens to start with.
The 5.6 will give you a brighter view on the groundglass.
Get yourself a good starter, learn the trade and the longer you practise LF, the more you read, the better you will know what kind of lens you want to buy.