I went the extra mile and spent about £70 UK on one. I have had the cheap ones before, and also have a Bluetooth one that I used on the Android (but have an iPhone now).
I am glad I spent the extra. It does loads more than the cheap one did, and has worked on every car I have tried it on.
Paid for itself in savings from garage diagnostics already (on the wife's car!)
I would post a link to one like it on eBay but not sure if this forum allows that.
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Basically, I am a techno-whore