At the price they are selling and the fact most people have smart phones, it's a no brainier for me to have one laying around... I keep mine in the glove box, so it's always handy as I have heard from way too many friends that panic when the check engine light comes on and end up paying $75 to find out their wife/kid didn't tighten gas cap when they filled up...
Ah the dreaded large vacuum leak or small leak if it's half on
, they are handy if you know how the emissions system work's but in the end they only steer you in the right direction for real problems it takes a lot more troubleshooting to find the real problem
