I had this lens when I was still shooting Oly OM...
From what I remember, the lens was very sharp for a zoomlens, but had a lot of distortion at both 35 and 105 setting. Other than that, I was very pleased with the optical performance. A little soft wide open at 105, but for the rest, quite good all things considering (f/2,8 3x zoom.) If you are going to use it for portrait it should fit the job!
It is not very compact nor light weight, but it isn't the heaviest lens neither... And it's quite a rare lens. I didn't encounter one for quite some time.
You could also consider the 28-105 f/2,8, which is also available in adaptall II. From what I've read this one should be even better. I had the opportunity to pick one up some time ago, but let it go. Still feel bad about that...