I grew a lot of kabochas this year - mostly unknown seed from store-bought squashes. There was a great degree of variability and while they all looked like kabochas, the quality was too variable for my preference. Some were great, but too many lacked top-notch flavor.
I had been reading good things about tetsukabuto and found some reasonably priced seed mid season, and planted 6 seedlings out around Aug 1. We have a long season (It's been sunny and in the 80s this past week) so I thought I would give a few a try. Even late, I found the vines to be far more vigorous than the other kabocha types I grew. I have not yet tasted the fruits (they are still on the now-ratty looking vines) and then they need to cure. They certainly won't be as good as full-summer grown, but I'm looking forward to trying them. Maybe at Christmas.
I personally prefer the dry-nutty-sweet kabochas and hope the testsukabuto grown here in SoCal lives up to it's press.
A follow up. The hybrid tetsukabutos are now my favorite squash. I would not call the ripe orange flesh particularly 'dry', but they are wonderfully flavorful. The skins are not tough and their texture adds to the eating experience.
They do very well here (frost-free foothills, SoCal, the avocado belt) and taste better than others I have tried (which isn't that many). The vines are vigorous and grow late into the season. With proper watering, I suspect they would keep producing quite late, but with no summer rains, that's not always an option. They also keep extremely well. Last year, even with the drought, it was one of the few things I grew. This year I planted even more, and with heavy mulch, I'm hoping to get even more.
Southern California, Frost-free coastal foothills, Zone 10