Ever since the NES, Nintendo consoles always have a ton of accessories and it's often hard to tell what's worth getting. The Fixture S1 allows you to attach your Switch to the Pro Controller but is that something you'll want to do? Well... absolutely!
I have large hands and find that playing Switch portably becomes rather uncomfortable after a while. Plus, the fact that your hands must be so far apart due to the substantial width of the console takes a lot of getting used to. Whenever a portable console is uncomfortable like this, I usually purchase an ergonomic handle that I can snap the console in. However, the Fixture S1 is a much better solution as it allows you to use the near-perfect Pro Controller on the go by simply attaching your Switch to it. On top of that, it has 2 rotatable joints along its arm so you can experiment with various positions and angles until you're completely comfortable. With that being said, the Pro Controller, Switch, and Fixture S1 add up to a solid amount of weight so I wouldn't recommend using it while walking or standing.
To set up the Fixture S1, you simply slide your Switch into the holder which connects via the Joy-Con slots then push the Pro Controller into the clip. After you have it all attached, it's quite impressive how sturdy it all feels and even after making adjustments, everything stays in place beautifully. Of course, I've only been using it for a few days now so I have yet to see if it will wear over time and if it ever does, I'll definitely provide an update to this review. For now, I'm very happy with how sturdy, secure, and adjustable the Fixture S1 is. My only quibble is that the Pro Controller sometimes isn't centered perfectly when you snap it in so if you're fussy like I am then you'll end up pushing and pulling it until it's perfect every time you attach it. Other than that, it's a fantastically put-together product.
Oh, and before I wrap this up, I should mention that you can use the Fixture S1 as a console stand which, if you angle it correctly, is much sturdier than the flimsy one that's built in to the Switch. The Fixture S1 also has a hole so you can plug a USB charging cable into the Pro Controller without detaching it which is a nice touch. They really thought of everything, didn't they?
So, is the Fixture S1 worth it? If you find playing Switch portably to be uncomfortable at times then yes, definitely. So far, I've played with it in bed, in the tub, on the couch, and whether I'm on my side, back, or sitting down; it's been super-comfortable and impressively sturdy. Plus, the fact that you can extend the Switch with the Fixture S1's arm means that you can cover your hands with a blanket if you're cold and poke the Switch through which is something that I discovered last night. In other words, it's a pretty cool device.