I will say: "as long as it works"
The install method for CM9 and AOKP is identical.
Also note that CM9 Dev thread said:
Normal install :
You need to have a kernel with CWM Recovery
Get the zip from the above download links
Put the zip on your sdcard, reboot into recovery, and install the zip
It'll reboot a few times during the install, that's normal
What does that tell you? Sounds like boot loop, right? Yes, it is the same.
Coming from BML, it will throw you to recovery.
If you come from Overcome, you will notice that the CWM is no longer Overcome's one, it may say HumberOS or whatever.
That is what the first install done to you. So proceed with second time install and you will be ok.
Again, as long as it works.