My first mount was a RAM quick grip. It was perfectly easy to use and great, but it got damaged in a wreck and at the time, I couldn't get a quick grip anywhere, I think they briefly weren't offering it, so I got the X grip.
I still have the X-Grip, been using it forever without problems, but I have to say, I also do use the rubber tether with it when I do use it. At least with the tether, it's perfectly secure.
However, there are some downsides:
• The phone I have now is a Google Pixel 5 and the power and volume buttons are on the same side of the phone, so I have to kind of guide the top right arm of the X to a narrow area in-between the power and volume up button, which is only slightly annoying. Could be an issue depending on your phone's button layout, also eliminates the ability to set it in the grip higher or lower if you want.
• The rubber tether covers the corners and in the top right, that means it covers up the battery life indication, and the top left, covers up the time. A minor annoyance.
• You have to use two hands to mount or dismount the phone, you simply cannot do it one-handed. Especially at stops if I need to go in for food or the bathroom, I don't want to leave my phone on the bike in the parking lot. This is a major annoyance/downside to me.
If you're deciding between the Quick Grip or the X-mount, get the Quick Grip. Once you set it up, you can put your phone in or take it out with one hand. It's much faster, easier and more versatile.
However, there are other mounts out there. Ciro 3D makes an assortment of adjustable mounts that look like they can be operated with ease with one hand.
I personally am not a fan of the quad lock stuff like Rokform. For one, it means you have to use their phone case, IF they make a case for your phone, which are inherently bulkier than other cases due to their design. And if they don't make a case for your phone or you don't like their case, or if you don't want a phone case at all, you have to put a case on then put on their universal adapter, which sticks out from your phone. And then if you get a new phone, you have to buy another case. Want to borrow someone's phone for whatever reason? Can't unless they also have the same quad lock setup.
To me, none of that is acceptable. That being said, I am sure those quad lock type mounts are perfectly secure, and the people that do have them love them, but I don't see paying $50-100 for a mount to have to pay $20-50 for a new case or to modify a case as being all that worth it when I could pay $50 for an equally secure mount that lets me use ANY phone with any kind of case.