I have an Xtension upright arcade cabinet from Rec Room Masters. It uses an X-Arcade Tankstick for control. Stella works extremely well with the Tankstick's default MAME keyboard mapping, if you do the following:
Use Stella 4.5-beta2 or later. You can find the beta2 build attached to this post.
In Options > Input Settings > Devices & Ports, deselect the "Use Control key combos" checkbox item. This allows 2-player games to work without the Tankstick's P1 key mappings triggering various control-key sequences in Stella.
In Options > Input Settings > UI Events, change the Move Up, Move Down, Page Up, Page Down, and Select item actions to the Tankstick events of your choice. I use the left joystick for up/down, the right joystick as page up/down, and the left-side primary button for item select.
In Options > UI Settings > Misc., change the "List quick delay" drop-down to Disabled. (This requires a restart to take effect.) This allows your event mappings from the previous item to work properly without attempting to snap the game list to that letter/number.
Stella uses the trackball as the P1 analog paddle, but it's not very sensitive by default. In Options > Input Settings > Devices & Ports, increase the "Mouse paddle sensitivity" to 15.
I hope this is helpful!