No guards, no nothing, that's correct. but you could write a nice little C# wrapper for it. 
Just for the fun of it, would you mind running your .dll through reflector to get a peek at the generated code?
Just for the fun of it, would you mind running your .dll through reflector to get a peek at the generated code?
Sure, but why me?
Ok, I used ILSpy.
I didn't have your code compiled and I'm on vacation, so don't have all my tools handy. But looks like single pinvokes per call. So it's all good.