I think No-ip sound very shady...
April 2013: the OpenDNS blog reported that no-ip was the second most popular dynamic-DNS site for malicious software. http://labs.opendns.com/2013/0... -- No-IP responded that they have a very strict abuse "policy", and they want other people to help by reporting violations of the TOS to them. They also scan daily and filter by keyword. http://labs.opendns.com/2013/0...
February 2014, the Cisco blog reported that no-ip had risen to be the worst offender: http://blogs.cisco.com/securit... -- No-ip again responded that they have a strict abuse policy, and they want other people to report violations of the TOS to them, and they scan daily and filter by keyword. http://www.noip.com/blog/2014/...
Were no-ip doing a good enough job at policing themselves? It doesn't sound like it to me, not at all. It sounds like they have a decent "policy" but don't go out of their way to enforce it, their daily manual scans aren't up to what's needed, their keyword filters are easily bypassed. They can sound hurt all they want that OpenDNS and Cisco and Microsoft wrote public blogs or took action rather than reporting the individual offenders to No-IP first. But the fact that No-IP does so badly, and got worse, shows they weren't taking adequate action themselves.
You say they're "very responsive" to reports of abuse. But honestly, if their strategy for combating abuse rests SO HEAVILY upon volunteers to report abuse, and their strategy hasn't been working so far, then they have a bad business model.
Disclaimer: I work at Microsoft, but in an entirely unrelated division (I'm on the VB/C# compiler team).