You can't use it without the straw and you have to use the straws it comes with or it will leak, even if it seams like the same size. But other than that it's a great replacement for the usual cap. I know it sounds simple but I love it because I'm always trying to find ways to get myself to drink more water and the flip straw rather than having to unscrew the cap makes a huge difference in my water intake.

This is exactly how they original lids were designed, then they went to plastic for almost all models.
The plastic ones have a thin flat gasket and not an o-ring. It's super hard to get it to come out for cleaning. The plastic ones also are made of two parts that are snapped together in the factory. This is NOT a water-tight seal. So gunk gets inside and is a potential health problem. I drilled a hole in the plastic one and gray goo came out. The entire design of the plastic lids is faulty as cleaning is almost impossible.
This, though, is all stainless steel. No seams or ways for water to get inside.
It also has a standard o-ring that takes a second to remove and wash. This is also a normal industry-standard size.
This is not a knock-off, but made by Hydro Flask/what came on the original model years ago and now is a replacement part. I think they sell one or two models with the stainless steel lid and everything else is plastic.
This is a mandatory upgrade that will make your flask last 10-20 years without health issues.

If you’re anything like me, your water bottle is basically your emotional support accessory — but the original lid? Not always the friendliest when you’re trying to drink on the go or during a Zoom where you’re pretending not to drink on the go. Enter: THIS lid.
First, the dust cover is genius. I didn’t know how much I wanted one until I had it. No more mystery crumbs touching the mouthpiece. No more “Did I just sip my own chapstick?” moments. Flip, sip, done.
It comes with two long straws you can cut to size (teacher hack: kitchen scissors work great). The handle is soft and flexy, making it easy to loop on a finger when your hands are full — which, let’s be honest, is always.
It also fits basically every standard-mouth water bottle ever invented: Hydro Flask, Iron Flask, Simple Modern, Klean Kanteen… if it’s 1.7 inches inside, this thing probably fits it better than my jeans fit me after Thanksgiving.
The lid feels durable but not bulky, doesn’t leak, and the flip-top makes it ridiculously easy to use one-handed. Great for workouts, car rides, or just surviving another day of “teacher hydration goals.”
Bottom line: If your water bottle needs a glow-up, this is it. Highly recommend.

This was a Christmas gift for my daughter, and she uses it every day. Quality product, arrived quickly, and would buy from this seller again.

It fits perfect! Looks exactly like the picture. It does unfortunately leak a lot if your bottle is tilted, so you really have to keep your bottle upright at all times unless you want all the items around it to get damp.

I am not sure why this doesn't come standard. I am sure it probably has something to do with adding revenue, but it is so much better than the cap that comes with the bottle. I like this because it makes it easy to drink one handed. I am a HS principal, and I carry my Hydroflask around on duty with me. This make is easy to get a drink without having to find a place to drop my laptop and anything else I might be carrying with me. It cleans up well. It is not 100% leakproof. It will leak if you hold it upside down or shake it. Not huge amounts, but it does leak. I made the mistake of leaving it in my backpack on a flight to Europe last winter holiday. It sat in the overhead on its side for 8 hours. It leaked all over the overhead, and was sloshing around. My family was the only one that had luggage in that bin, so the only was the only looks I got.

This accessory straw top is great. So much better than the other brands that "mostly" fit but aren't Hydroflask. It doesn't leak when it's closed, easy to get the straw in, and best of all doesn't have that soft rubber on the flip lid that breaks down so quick and isn't easy to clean. It's worth getting the name brand that was designed for this bottle.

It is what it is. No surprises or shocks.