Straight loads, just like a stock trailer, have thier advantages and disadvantages. I have had both, but now with 4 horses more is better.
The first thing you need to consider, "Will my horse even get into that tiny trailer after being used to a large stock trailer??" If you don't know, have them bring the trailer to you to try or borrow someones like it. If you already know your horse will load, or you are decided that you will just teach him to load, then think about any other uses. Is there ever a time with the large trailer that you can think, "Wow I sure am glad I have a big trailer for this exact reason..." then maybe you should go with a 12-14ft stock trailer instead.
In my own case, I rarely ever pull more than one horse at a time but my trailer is a 16ft convertable slant load to stock trailer with completely removable dividers, short wall, and saddle rack. I wanted it specifically because of the ONE time I had to help my father in law move cows and because ONCE a year I go to a trail ride that I might haul an extra horse for a friend. So I wanted the extra room, and there hasn't ever been a time that I thought, "geez, I just have too much trailer!"
Good luck in your search, that looks like a decent lil trailer to me, make sure to check your axles and ask when the last time the barrings were repacked, check floor boards...
One is closer to God's heart on a horse than anywhere else on earth!