I held off on replying, as I have no personal experience using them. I have parallel bars made from 1.5 inch steel pipe in a wood frame. But since you asked, here's my thoughts.
There are a few YouTube videos of guys doing weighted dips on tall parallettes, and it seems to work fairly well. I would be somewhat cautious about lateral stability - one video I watched showed one of the bars tipping sideways a little at the end - but that seems like the only potential issue. Everything I saw regarding that Lebert set was positive other than the cost. They look to be quite well-made and solid, and I have no doubt that the weight rating is a conservative one. The reviews on Amazon are also quite good. If you are okay with the price and you won't exceed 400 pounds, they should serve your purpose just fine. Go for it!
BTW, don't overthink it too much. Just because you haven't seen anyone else do something doesn't make it questionable. If you're sure it's safe and it suits your needs, adapt it to your use and don't worry about what anyone else does. I have a barn filled with a weird combination of purchased, scavenged, natural, and DIY gear for traditional weight training, strongman, calisthenics, Parkour, Scottish highland games, etc. Although most people think my training is bizarre, I enjoy myself and am seeing fairly good results in strength, athleticism, and body composition. I could do more traditional training with more standard equipment, but that's just not my style. Figure out what you want to do, get (or build) what you need to do that, and get after it.
I hope that helps, and I wish you the best with your training.
pathfighter wrote:Keep at it. People may not listen to regular madmen, but they do listen to jacked madmen.