For the non-mechanic like me, the cheapest one that allows you to reset the check engine light.
I bought mine some years ago when my Subaru Outback’s dashboard lit up like a Christmas tree and disabled the cruise control. I still had 200 miles left before home over empty desert roads. I went into an auto parts store and bought mine, costing me about $45. My Subaru’s gas cap wasn’t tight enough. I tightened the cap, reset the check engine light, problem solved.
I’ve not used mine on my T4R yet.