I can't speak to the BS100 GMT directly but I have owned the BS300 and BS500 in the past, both were fantatsically built watches and infact I still kick myself for selling the BS500.
They're on the chunky side but it's all part of their charm, and the GMTs do offer that splash of colour which makes them an excellent choice as a summer watch, especially on a coloured Isofrane strap.
They're sometimes available on pre-order so you can get a discount that way, otherwise I'd say used would be your best option as you'll likely save yourself up to 50% or RRP.