For me, I'm using an iPhone 11 Pro Max. This power bank is perfect for my phone because apple limits the iPhone fast charging to 18W. 18W is also the max output on this charger via USB C. On days with super heavy usage, I can plug this into my phone via a USB C to Lightning cable (Sold Separately). I don't let my phone die completely. I usually start charging it at around 30% or so. After putting it on the charger, I can expect my phone to be around 60-70% in like 30 mins or so. It's great for when I'm in a pinch. The device itself doesn't take long to charge either. When I first got it, I think it took about 2-3 hours to fully charge it. The power bank was at less than 25% charge out of the box. Some people might think this is bad, but it can only charge so fast. My iPhone takes about 1.5-2hrs to charge from 0%. The iPhone has about a 3,969 mAh battery. This device taking about 33 pct longer to charge with 2.5 times more storage seems decent to me.
Something I've noticed with this particular power bank vs other that I've own is if you leave a cable plugged into it it'll slowly drain the battery. Other power banks I've had in the past never acted in this manner. At first, I thought it was a defect, so I sent it back to Amazon. The new one they sent me also had the same behavior. Come to find out this is normal. If you're planning on storing this for an emergency, store it with the cable not plugged in.
Again this power bank is Fantastic. Fits in my jeans fine, and I don't notice it. You won't go wrong with this one.