I'm biased (cos I have two, slightly later ones).
The old Kohlerts are wonderful... In their day they were considered the best of the German/Czech saxes, although some prefer Keilwerths. Ergo's are, for me, fine. Light, fast. Intonation's OK, but you may have to work at it a bit. Yes it's Czech. Made in Graslitz (Kraslice in Czech).
I've never heard of Windsor Castle as a model and the ebay shot is terrible. So there's little to be learnt from ebay.
I found this from earlier this year:
http://www.worthpoint.com/worthopedia/kohlert-windsor-castle-alto-saxophone-244785161
Which explains a lot. Kohlert made a lot of stencils. And I don't know any other maker from that era in that area with a serial number list that'd match. So it looks as if it's a Kohlert, stencilled Windsor Castle by a brit seller.
I've no idea what the mouthpiece is. If you're lucky it's an old Brilhart, but it doesn't look like one.
Same serial number as the one on ebay... Assuming the repad is OK, you may need a couple of tweaks, but probably nothing expensive.
Looks like it's in Silver plate with a gold wash bell. Nice. Doesn't have the micro tuner neck (no loss, they seem to sieze up).
Serial number dates this to 1928, possibly 1929 / model 1928.
Mine was compared to a Yani, A Sax, King Zephyr, Buescher True Tone, Mk VI. To my ears (obviously objective), it was the best sounding of the lot. And my teacher, who owned the others, was really impressed with it as well... And I've compared it to some modern Far east altos. No comparison, the Kohlert wins hands down every day.
ymmv, and I'm sure a couple of the modern horn fans will say don't waste your money...