Anywhere to see where you registered your email?

That's what makes services like this dangerous...."safe" on the Internet is very very relative. The only way to keep information 100% safe on the internet is to not put it on the Internet to begin with, the best we can do is try to get as far away from 0% safe as possible.

The problem here isn't whether these guys know what they're doing or not, the problem is that they can't reach 100% safe any more than anyone else can. Say you have a Google account and that as long as you keep your login details private, enable 2-factor authentication, etc you reach a relative level of 95% safe.

Then you find unroll.me and for all intents and purposes they're also 95% safe so you feel ok with allowing them access. What happens now is that your own overall safety drops to approximately 90% safe because you've now introduced a little bit more "unsafe" because neither service is 100% safe.

Then there's another layer, the 95% safe with Google is only the technical safety (how hard is it for someone else to gain unauthorized access to your stuff from the outside?) and assumes that you can actually trust everyone who has low level access to Google's internal systems, likewise does it assume that you can trust all of unrollme's employees as well as your own computer, phone, etc. Again there's no such thing as 100% safe, there's always a risk that there is a rotten apple somewhere in the mix and the more people you add to your implied sphere of trust, the higher the risk.

(The %-numbers above are completely made up and are only meant to illustrate a point and thus they are not intended to be read as any kind of measurement of an actual risk level of any service or company. )