I have a pair of their bourbon glasses (the smallest ones) and use them frequently. They have a nice heft to them and accommodate the occasional ice cube.
The Island looks a lot like the riedel O and the lowland looks glencairn.
I'd go highland- the inbetweener.
In what respect is any of them superior to a Glencairn at half (or less) the price? (That's a question, as I always have to tell my wife, not a criticism.)