The opening is plenty firm, which I liked, as was the interior chamber but air captured inside after insertion had to be released...I slide my little finger along the side of my penis to release the air pocket, fully insert, and slide my finger out. Getting the air out of the very end was extremely hard. I liked the interior "S" shaped chamber. With my girth, the ribbed interior felt good but was too tight for me...it was hard to keep the lube in place because the ribs pressure kept "scraping" the lube off the surface of my penis and would quickly begin to be irritating.
I liked the grip / pressure of the Booster Stroker once fully inserted but given my girth and the shortness of the internal chamber, it just wanted to slide forward and pop off. I had to concentrate to keep it on my penis which was annoying but it felt good. I found this to be distracting the longer I used it regardless of the good sensations.
The Booster Stroker has an interesting feature due to a small(?) chamber at the end of the internal shaft. There is a final, smaller rib before a round-ish chamber, clearly for the penis glans to "enjoy". Initially, I found it pleasurable and different but quickly became sore. The following morning, my glan was clearly "bruised" and was tender for several days. For me, the chamber was clearly too small. It could be that this chamber at the end is for lube to collect and not to be entered. If that is the case, the insertion length would clearly too short for me.
Aside from that speculation, I could get my entire penis inserted but it was very tight, a tad short...I was stretching it laterally and lengthwise. It felt good for a very, very short period before the lube was "scraped" away. I began to like it was mainly designed to squish my penis down to the size of a hot dog!
I found the two "finger holds" interesting...for stroking action. Due to the "S" shape, the stroking action keeps the Booster Stroker in one orientation to the penis...rotating, twisting it, really does not work well.
I liked the closed end because it creates suction and provides an area for lubrication to collect.
I would be very interested in a similar model that is 10% and/or 20% longer...and, with an interior diameter that is, maybe, 10% to 20% larger.