I would guess the axle is about 2500 pounds, meaning it will carry up to 2500 with the trailer included. 1300 pounds of stuff. Not likely you will get 1300 pounds in it.
I am not a fan of the way they dropped the axle, but it should work fine for you in that weight range. The outer bearing set up should be the same as their 3500 pound axle. This particular style is made from 3500 down to 1800 custom ordered. If I were going to use it off road, I would stabilize the perches they sat the axle on, weld another bar between them or connect them farther up the trailer. If you have questions go to the Kelley build and look at my frame.
This axle is used by the US Military now on all trailers, so it should work for quite awhile if you keep it. Looking at the pictures, it does not look compressed so it is most likely in very good shape. As they grow older with weight on them they tend to push up towards the trailer. This one looks like brand new in that respect. Of course just looking at pictures.
Bob