Ease of opening doesn't apply at all to pressure barrels - these look more like Speidel fermentors, with a bottling bucket style spigot tap in the bottom, than like casks. Pressure barrels are far more available than cornys in the UK, too (Wilkinson's, a cheap home goods store, sell them, for example, as well as most LHBS). In the US, pressure barrels are completely unavailable, which is a real shame, as it's a cheap ($60 for a good one, with no other equipment required) way to condition and serve a 5 gallon batch of real ale.
This is a pressure barrel:
The main advantages of cornies in the UK would be the ability to carbonate in the keg, and to carbonate to higher levels (for US and European styles), the ability to put the tap remote from the keg and drive the beer by CO2 pressure, as in a kegerator tower or fridge door type arrangement, the fact that you don't get oxidation in the keg, the ease of cleaning stainless, and the fact that cornies will last a very long time relative to a plastic pressure barrel. Against that, it's much easier to cask condition in a pressure barrel, for English style real ale, and many of them now come with CO2 injectors to prevent oxidation. They are smaller and easily fit in minifridges (known as fridges to the UK readers
) without modification. If you only brew English styles, there's very little benefit (longevity only) to a corny setup over pressure barrels.
Another factor is that a cask serving beer engine ("hand pump") can be had in the UK off eBay for about 60 pounds ($100), so that's another solution to serving remote from the pressure barrel or cask. It's rare to find a second hand one here in the US.
I'm waiting on a CO2 injector/pressure relief valve from the UK to turn my 20l Speidel fermenter into a pressure barrel...
