This is a review of the plastic 3D printed Kali's Grip KTB, available from Playtime at Shapeways. Link - https://www.shapeways.com/shops/playtime There are 11 different designs available, and I think custom designs can be made on request. I chose the 35/5/03 - 5 rows model. This has in internal diameter of 35mm, 5mm spikes (making for 25mm diameter of free space), 0.3mm end of spike, and 5 rows. It is 2.9cm in length. This size was ordered as it almost perfectly matched my erect and un-erect penis diameter. I ordered mine in White Versatile Processed Plastic, which has the usual rough surface, though this is not an issue for a KTB. It is much lighter than the metal Chinese KTB, which means it is much easier to wear. It stays in place fairly well, though can migrate towards the head with lots of erect/un-erect cycles. Maybe I should have got slightly longer spikes? Getting it on is fairly easy if un-erect, but care needs to be taken to avoid pinching at the hinge and where it closes. If erect, it is almost impossible to get on. It is locked using a small padlock. It certainly punishes an erection with the feeling of lots of pin pricks, and I found that when any stimulation was removed it quickly deflated - quite a deterrent to staying erect! An orgasm in this, ruined or full, could be very uncomfortable! After removing at the end of a session, the only damage was a few tiny little skin abrasions and a small blood blister. This was all healed a few days later. For occasional use for punishment or CBT sessions it is good value for money, and I can't really fault it. A longer version would possibly be a good addition to the range.
My experience with these 3d printed KTB's are that they are quite good and effective for session play, but not for long term. After the arousal is over and things return to un-erect, mine has a tendency to slip off. I tried a smaller diameter, but when I "turtle"< it seems that I need the attachment to the balls to keep things secure. (It was pretty embarrssing when the KTB w?lock slipped off and somehow escaped my panties and fell to the floor in front of vanilla friends!)
I don't think I would use it for anything more than session play. However, I don't think this one would fall off too easily as long as the sizing is right. Must have been some loose underwear!