Peter, do you really think it is fair to say that you heard bad things about it when you just think that there must be a quality loss?
For sure there is a quality loss, but I have not heard anyone who can see it. It is not uncommon for good lenses to be able to handle a good 1.4x converter without noticeable loss of quality, and this is a 1.5x converter.
IMO the biggest problem with the HTS is not quality, but the fact that there are no lenses with which you can stitch to get more coverage than without the HTS. In other words, if you put the 28 on this, it becomes a 42mm. If you then stich up, down, left, right, you get 28mm back. That renders it useless for some purposes. Not for others though.