Yes I bought my first trailer from them. They get a good range of second hand trailers through their hands, so there is a good selection most of the time. They even delivered mine as they were passing. A couple of my friends have them for barlows too. Have fun!
I have my trailer serviced at Barlows, and had a look around one of their display 3.5t boxes (as you do).
I think I thought it was Ok, and certainly better than an Equitrek. I think that it has a wide rear passenger access door to the back? I like these (safer in case a horse comes over the breast bar). I have to say that I do not like 3.5t generally, but the Barlows one wasn't too bad.