I have got a 430 skinny from KA and it seems really good. Build quality looks to be the business and as I use KA sails they seem to be matched well. I think for the average joe sailer you would not tell the difference between masts especially skinnies unless you buy a real dog or try using a race mast wave sailing etc.
For the price and build quality I think they are great value.
Not a big fan of the old KA brand, myself. Try ezzy rdm, I dont think they are much more expensive, but I bet they'll last a lot longer.
i got the 370KA skinny for use with the koncepts 4.4 and 5.0.
havent used the mast on the 4.4 much as there hasnt been any wind for almost 12 months to warrant it but i use the 370 plus a tip extention for the 5.0 a lot more and it is still in 1 piece and works great with the sails mentioned.