Brompton designed the Easy Wheels to provide support to the bike when in its folded and resting state, and to roll smoothly on any surface. On why Brompton didn't install the Easy Wheels in all of its models escapes me.
But these things are expensive. They are $30/pair in the US, or approximately P1,300! Grabe naman, P1,300 for two 2-inch wheels! Mahal! But I really disliked the caster wheels AND the in-line skate wheels, so there was no other option but to buy the Easy Wheels. I asked my brother-in-law to bring home a set when he visited, and they have arrived.