Hi Esben.
I completely agree with you, and have myself been doing that kind of testing for over 3 years now as a “hobby”. From a testers (and test team leads) perspective it is also an interesting opportunity to be able to work with completely different software than one would otherwise be exposed to in normal work.
If you own or work in a small company, it might not be possible to hire a tester to test your own products in an early stage, due to the cost it introduces, thus the possibility of being able to “order” this kind of work from a dedicated group of people is something worth considering.
And for larger companies this offers the possibility to get a fresh view to your software from end user perspective.
Security testing is one special case that most companies don’t have enough knowledge on, so the more options there is (and cost-effective ones) to utilize outside service the better.
Mikko