I would say that depends on the park and the amount of space. Just my opinion, but I like some wide open space when I train. A soccar field size should do it. But it would be easy to go beyond that with those two planes. You would need to stay on top of the student to keep them close in. They tend to stray pretty far out quickly. We used to have a county park to fly in but because of one person, got us all banned for awhile. Then they let an electric only club fly there that lasted about a year. I dont see anyone flying there any more. It can be risky training with lots of park patrons wondering around.
I've not trained on a park flyer, but you hear of people saying they do it all the time. I just never see it at any of the clubs I've been to. I suppose if I were to guess, there is a parkzone (I think) thats a super cub with ailerons. I'm a firm believer that you should teach on a aileron capable plane from the beginning. I've picked up several students that started on toy planes and finally upgraded to more serious stable trainers and they absolutely loved it. Big difference. This all of course, is just my opinion.
Edwin