The little sight for Glocks? I don't have one but I've shot a couple. They're kinda nifty and they draw your eye right to the FSP. That's all I can say about that
I was going to go this route to "ease into" an RDS, as I think it'll be a shorter learning curve. But Holosun came out with their SCS which mounts directly to a MOS slide and is low enough to co-witness with the factory sights, so I just bit the bullet and went that route instead.
I think for an M&P or Glock they are interesting enough to try.