UPDATE1: Added a “Slim” version of the controller grip, the attached pictures show both grip types, the slim grip is slightly smaller/condensed if that suits your hands =)

UPDATE2: Added a “Prototype” version of the slim controller grip, that has a space in the handle to store the dongle, there is a multi-color and single-color version, also depending on your combo of fuzzy skin/material settings, you may have to file the dongle holder a little bit. Try putting your dongle in, but only half way, if there is too much resistance use a file (what i did) to file the rear of the slot where the dongles grip interfaces with the dongle holder, until your comfortable that it slides in/out.

A quick controller grip for the Atari CX78+ Wireless Gamepad. My first 3D design that I am sharing, excuse my skills, I'm only a novice but I think the print came out great :)

I saw a number of these models online as paid models, but for me the paid models cost more than the controller itself :/ As I am a novice, I realise the grip doesn't look as cool or as fancy as other contributors but I'm sharing this freely, if its of any use to you, then that's great.

The Controller Grip has cutouts for the the front led's, sync buttons and the USB C port, for easy access. There is also two indents, matching the two fire buttons. 

For ergonomics, it's really going to depend on your hand size, for me the controller grip is just right. It's a friction print, so the gamepad is held in naturally, it's not loose on my printer, but I have a version with a clip, if you need it. I used fuzzy skin (as pictured) and it sits just right. There is a oval cut-out on the bottom of the controller grip to allow easy removal of the gamepad.

Print Settings (as pictured):

Infill - Left at default 15%

Supports : Normal + Baseplate only

Fuzzy Skin : 0.2 point distance + 0.2 skin thickness

Material used: Matte PLA

One final note, with a controller grip on the Atari CX78+ depending on your finger size, it may be a stretch to reach button 1, this is more a symptom of the gamepad design, and any controller grip should have similar ergonomics. I guess some sort of one sided controller might work for those people? Let me know, If that's something useful, happy to create some variations of the model :)

P.S this is for the new Wireless controller, I'm not sure if this would work with any other model, like the original, etc.