I was just looking over the specs for the hobby eagle A3 Pro and I didn't see anything out of the ordinary. I find it odd that you are limited in your rate selection. I have some gyros, from other brands, on some of my planes and I have high and low rates accessibility.
I think you should recheck your tx settings and be sure that it's programmed correctly. What tx are you using?
Like I said, above, I just find this behavior to be odd because the unit that you are using is simply a "flight stabilizer"....similar to what I use. The flight stabilizer shouldn't keep you from using high and/or low rates.