You passed the first test: I asked myself "wait, how is this not a one-stop-shopping service for aspiring, technically incompetent DOS attackers"? And I found your FAQ and answered that question inside of 45 seconds:
I went through your registration process, and got nothing. Very disappointing - the type of thing that will make me never look at your website again and scoff about it to my friends should they bring it up.
And a couple other nits:
1) Your registration page where I choose my plan type is not intuitive. Maybe it's because green is not a good color to call attention to stuff.
2) Your Register and Cancel buttons should be different colors. I clicked the wrong one and had to redo my registration.
3) Don't ask for number of employees and industry. They're not required and they will hurt your conversion rate slightly. And it indicates to me you might sell my data.
Employees and industry is there for us to learn who our customers/users are. This is a new type of service, and we need information on who are target audience are, because we frankly don't know that yet. These values are optional to fill in, though. Should we be more informative, maybe, and tell people that we will absolutely not under any circumstances give out information about them to a third party - would that reassure you?
Finally, your confirmation email might have been delayed as there was a DNS issue yesterday that caused outgoing email to be queued for a while. Apologies about that too and thank you for the feedback. It's very nice of you to give it even though you weren't happy with the service. Negative (but constructive) feedback is the most valuable of all for us.
(Its a DDOS in a can if you have a few dozen people capable of reading directions.)
You probably don't want to do this because it would make the process much harder, but you can allow it in reverse; claim to deny load tests for a domain.
I'm guessing that you want to give a "live demo" to people, but I'm sure you could just show a demo report of a couple sites that have already been tested.
Example: the test starts by simulating 10 clients. The average page load time measured is 500 ms. The test then moves on to test using 20 clients. If the average page load time goes above 1 second (twice what it was originally), the test will be aborted.
We have a general security philosophy that is based on different levels of trust. An anonymous user is trusted the least, a registered but non-paying user is trusted a little bit more, and a paying user is trusted even more. The level of trust determines how often you can run tests, how much data your tests are allowed to transfer, how often you can place load on individual destination servers (IPs), what settings you can make for your tests, etc.
First of all, you're admitting that it's okay for anonymous people to inflict a significant, measurable delay in page load time for my entire website. That is completely unacceptable.
Also, while I'm sure your system is well designed, it probably isn't perfect (because nothing is). If your monitoring service malfunctions then the tests might never cut off.
There should only be two levels of trust: people who own the server (and can test it), and people who don't own the server (and can do nothing to it).