My sister-in-law has the Secret and the saddle is not as low as you think. I agree I wouldn't buy a bike without a test ride, but just passing on my findings to you as I tried a lot of Kudos bikes.
Are you able to get to their HQ (nr Herne Bay,Kent)? We went there and you are able to try as many bikes as you like. The staff were really helpful, nothing was too much trouble and not at all pushy.
Guys,I ride the Secret,am 6ft and long legs and find it comfortable but one of my employees is a sports cyclist and rides these folders with a different attitude,he wants the bike to feel like his sports bike,I want it for hopping down to the shop to get a paper. Peter Eland of the Electric bike magazine also commented that he found the saddle height too low but he is also a very tall guy.
Anyway,the solution is simple to have an extended length seat post,I have asked the manufacturer to
supply a quantity of seat posts plus 100mm. The only problem is that it extends the bike beyond its folded envelope and may be a bit of a squeeze in the transport bag.
Have just looked at the photos on our website of the Secret,the seatpost is very immersed in those photos it extends a lot further out than those photos would suggest.
However,the post must not be extended beyond the minimum immersion depth(indicated by etching on the seat post),for extra height the extended post will be necessary.
Hope that helps.
Dave
Kudoscycles