My 100E has them fitted, infact mine are actually the very rare turbo tecnics versions as fitted by them on some of their TT capri conversions.
the only difference with them compared to a princess caliper is they have had the galleries internally drilled so only one external pipe is needed.
as for how they work, yes there heavy but they stop my car far far better than the old m16 vented efforts that were on there..
they are getting rare now and go for good money on ebay..

steve