2.5 rounding up. If you're a super die-hard ST-TOS fan, your mileage will vary.
I always liked the Star Trek episode "The Trouble with Tribbles," but I always thought it was an odd episode compared to the others. It stood out as having a more physical comedy element to it compared to the rest of the series.
The first part of this book is an excerpt from Gerrold's Blood and Fire, which was mildly interesting; however, am introduction or explanation about what I was reading on the front end would have been appreciated. It took several pages for me to realize it as a sample of a completely different work and not an early seed story for the Tribbles script.
After this inexplicable sample, Gerrold goes into his personal history about being a sci-fi nerd in mid-century American when that sort of thing made one a bully magnet. Finally, we get to the history of how the Tribbles story came about and Gerrold's experience as a newbie writer trying to sell a script to the hottest new show on TV. He admits his success there can be attributed to being n the right place at the right time and plain dumb luck. He explains the way a story pitch becomes a TV show (or at least how it worked in 1968) and divulges his version of the behind-the-scenes activity. He also provides information about what can and can't be done with a story on a low-budget show. It's interesting to see the changes the story went through and why they were required. In short, television in that time didn't care one whit about quality; it cared only about formulas, format, and ratings.
And, yes, he indulges in some hero-worship of the show actors, mostly sugar-coating his experiences with them. Why anyone would hero-worship any actor, but especially William-frickin-Shatner is beyond me, but to each his own.
One unintentionally amusing part in this book is the author explaining fandoms. Anyone under the age of 40 should note the book's original copyright date of 1973 rather than thinking Gerrold is explaining the obvious. Pre-internet, people kept their obsessions a lot lower key rather than broadcasting them. I only half-joke when I say the internet has ruined damn near everything.
Speaking of fandom and, by extension, the hyper-excitable and uber-invested people of which they are comprised, apparently there are some rabid vintage sci-fi folks out there who are outraged -- OUTRAGED! I tell you -- on behalf of Robert A. Heinlein based on their opinion that tribbles bear a strong resemblance to the flat cats in the RH's book The Rolling Stones. Yep. Sure do. And the parties involved worked it out, even if their versions of exactly what "worked out" means are slightly different. But, come on peeps, this was over 50 years ago! Frothing at the mouth bout it in 2020 just makes some people look like they need to adjust their meds. Let it go already.
Gerrold does now say by what criteria he claims TTwT is the most popular ST-TOS episode, so we can only assume that part is author subjectivity. He admits his ego is huge, and TTwT is his baby. For my part, I'd go with "City on the Edge of Forever", "Amok Time", or maybe "Mirror, Mirror."