MartyClayton The QS-S4 throttles are generic units that come with either the standard trigger or increasingly popular thumb throttle version. You should be able to swap the thumb throttle unit into any scooter that is using the QS-S4. The majority of new scooters on the market that use the QS-S4 have plug and play connectors so installation should be quick and easy. Almost every retailer, is carrying the replacement QS-S4 thumb throttle as an optional accessory.
As for horizontal vs vertical movement, I haven’t seen any obvious drop-in replacement throttles for the QS-S4 that are vertical like the Ninebot Max, Air, etc. VORO has a twist throttle for their EMOVE Cruiser, but I don’t think it’s necessarily drop-in compatible with anything else.