I wanted to upgrade from the eyepieces which came with my Starwatcher 130 and plumped for the 12mm. The image is excellent and magnification up from the 25mm. The rubber surround is adjustable for eye relief and as I wear glasses I tried it in various positions. Pushed inwards it gives fairly good eye relief. When I tried to attach a smartphone I had difficulties - it wouldn't focus. Then I managed to take off the rubber and hey presto the smartphone fitted perfectly and focused well. I assume the rubber is to protect the glass but even with it off there was no contact with the phone lens and the eyepiece glass.

I am a complete novice, only really starting out.
However my telescope a Skywatcher, Skyliner 200 p came to me secondhand along with an original eyepiece. The standard eyepiece gets you going, but compared to the Starguider BST you notice that firstly the overall quality just seems so much nicer. It's heavier and more solidly constructed. In comparison the original eyepiece seems a lot more cheaply made!
I have only used it for a short period, but found it's easier to work with, and with my limited experience can't really tell you anything technical about it, but I do like it, and is a vast improvement over the stock eyepiece.
I did a fair bit of research, others liked it on other forums, and recommended it. I do the same. It's good value for what it is, and not too expensive. I will buy the others I need in due course of this make!!

This is my workhorse EP in my 120ED Evostar pro, very good quality but more important extremely sharp views, its hard to think of an alternative that does not cost 2-3 times the price of these, i had the 18mm a while back and found it hard to tell the views apart from a Baader genuine ortho 18mm. If your looking for a decent eyepiece and cost is important give these a try