The only con I’ve had with glue ons is the cost.
So my horse is a chronic shoe puller, and a little over a year ago he started losing shoes CONSTANTLY. Of course each time he lost a shoe, a little bit of foot would be gone too. Not much to start, but as time went on it got worse and worse. We tried a bunch of different things (different trimming, bell boots, etc.) but by that point his feet were just too damaged to hold nails and a shoe.
We started him in Polyflex glue ons and I haven’t looked back since. He’s more sound, and he never has any issues with them. He doesn’t pull them off, and he doesn’t need bell boots anymore. He lives out 24/7 in PA, so every kind of weather and footing imaginable. The glue holds up through everything, from wallowing in mud to dry hard ground stomping at flies.
They make a version with pre drilled stud holes in case you need them. I will say that without studs they can be a little slippery on wet or long grass going down hills, but they do have a toe grab as well that helps.
Not every farrier can do this specific brand, but there are a lot of different glue on options available. The only downside is the cost–they are very expensive. It’s worth it to me for his improved hoof quality and keeping me sane (I never worry walking out to his field “did he lose another shoe…”)
He’s never had pour in pads, so I have no feedback about them.