In my mind, what's saddest is that those teachers who could rethink their teaching strategies a bit are probably not the ones who will do so based on such a site.
Of course, it's a bit like course evaluations in universities. But these are less targeted and quite likely nastier. Like course evaluations, it can be difficult to read some of these comments. "You need a tougher back!" Well, maybe, but we also need other ways to assess the quality of teaching.
As anything online, nobody will be able to stop this. But we can certainly find more appropriate ways to evaluate learning, teaching, and collaboration.
As for what's more difficult. It seems to me that it depends less on the clientèle than on the overall
context. Have only taught universities, so far, but some of the most difficult contexts were the ones in which there was an incompatibility between my teaching and the students' approaches.
As is often the case, it's quite difficult to tell who has it easy.