I don't see the closed ends as a detriment to the design. We probably mostly all run the rear RCM cover and do something to cover the holes in the front to prevent dust from getting in anyway.
I've got a 1509 and 1512 and the Tekno 1515 and I don't notice the Tekno motor spinning more easily by hand at all. Wish I had a 1515 to compare it to.
I can tell the Tekno 1515 has definitely got some more kick than the 1512, temps are lower, Amp draw is about the same (which makes sense - 2050kv for 1512 and 1700 kv for 1515). I am a happy customer.
My only complaint is the pre-attached bullets, took me an extra 2 minutes to unsolder them to put on the 6.5mm ones.
