If Angel recommends them, go for it.
On the difference, that is quite interesting. Here in Vancouver the potted plants are much more expensive than the non-potted. For instance, the common sword Echinodorus bleheri will sell for anywhere from $9 to $18 if potted (depending upon the store). Bought tied together (the non-potted), I can get them for $5 and there will be 2 plants tied together. These will be very small, and obviously less root systems, but most of the plants in my 115g in the photos are these non-potted plants.
The potted in the photos on that site indicate what Angel said, the potted will be larger with better root systems, so given the same cost, I would go for the potted. However, they will likely be single plants, and the tied ones might be two plants.
I think a couple of the local stores here get plants from those people, the name is familiar. I may have their plants in my tanks, some of them anyway.