I have mixed feelings about them. I had one of the early ones, which came with my shetland mare when I bought her. She had been started off in it, and at that point had never been driven in anything else.
On the good side, they are very light weight and easy to get in and out of. With mine, two adults were a bit of a squeeze, but I think that's better now with the newer models even with the shetland size. I sold mine to a friend with an elderly shetland, and he is happier in it than his former exercise cart. However, he (the pony) is longer bodied than either of mine, and she did have to have the shafts extended a little for safety.
They give a very smooth ride on the roads, but because they are so light, they are very bouncy off road, even on grass or school surface. I tipped out of mine when doing an involuntary sharp right turn in the outdoor school! It does say in the Robinsons catalogue that they are designed for use on paved roads - and they have weight and speed limits!
I found the tyres went flat easily, and I had a couple of punctures. In the end I decided it wasn't suitable for what I wanted.
So, in answer to your question, it rather depends on what you are going to do. If you will be doing a fair amount of off-road work, even if it's just in a field, you may be better off with something else. If, like my friend, you will largely be sticking to roads or lawn like surfaces, it will probably be fine. Hope this helps!