Ranked in these QuestionsQuestion Ranking
Pro Simple and friendly UI
You just need the URL and the User-agent. Very simple
Pro Choice of User agents and Bots
You can specifically view based on user agents.
Pro Text Feed Back
The Drained only text feed back is a real plus. If you do hidden in css you wont see it in text feed back. thats great for a SPA.
Pro It Fast And Free
Its online, so you are testing from another server minus your own firewall and internet issues. Its Free. I used it to test my some of my website thousand of times.