Their website is very easy to use and handy how you can cross reference stuff on it. Sometimes that also helps make sure you get the right part.
Biggest complaint I have about summit and amazon is unless you know the exact part you want their sites are a pain to use. It's more understandable with amazon since they aren't in the car part business.
The problem I've had with some other online parts stores is that they show everything in stock then once you've made your order they tell the part isn't available. OK that's understandable since they might be drop shipping or bringing a part in from another source. But then even when it's known they don't bother updating their website.