Every time I buy the LG 5K I feel a little sad (it's overpriced for what it is, outdated, and limited with non-Macs), but every time I use it, I'm happy with the purchase.
Biggest downside (aside from the price) is extending the Apple lock-in.
As mentioned elsewhere, it and my mac are sensitive to the cable, so it's worth trying a couple if they give problems. (More apple idiocy: what if we put the same connector everywhere, but made devices super sensitive to some qualities of the cables, connectors, or who knows what -- there's definitely no way this will be super confusing for users!)
Biggest downside (aside from the price) is extending the Apple lock-in.