Their charting is generally good. I like being able to force the app to check for sales stats whenever I want. It's not automatically updated (on the free tier). They also break out educational bulk purchases which is great.
If you go beyond their free tier, the pricing is done per-app but with a discount for the free tier. I've been close to subscribing three times and could never figure out what I'd be paying for 10-12 apps. I'd much rather just have tiers. Something like up to 25 apps from a single publisher ID as a middle tier for $5-10 a month would work.
If you're in the iOS App Store, you need to at least try the free tier.
Sales figures (but only for a subset of our apps). I can generally get sales figures through them before any other sales figure webapp. Breaking out educational bulk sales is very helpful to us.
The charting options with cumulative sales, stacking, etc. lets us get a good feel for trends and helps stay motivated.