They can be , yes. I don't use them because I consistently play in freerolls so my variance in hands always is different. To use them for other players , Meh I prefer the good ol fashioned wait em out and find their ways of play.
I used one called PokerCopilot for a while,I began to observe things I did not know,I think it's a valid experience. The rooms have a list with the Softwares of this nature that are accepted, when you find some check the list
Hand2Note is free up to tournaments with a buyin of $9 and above i think. Its pretty good because it sets up databases and stuff for you so its ready to go after a simple site configuration.
Be aware though reputable Antivirus companies are finding viruses in the program BitDefender, Norton, Trend Micro, Ad Aware etc etc. People affiliated with Hand2Note are saying 1) they are false positives 2) The reputable Antiviruses are not finding anything.
Its a little hard to believe because the aforementioned Antivirus companies are some of the best of the bunch.
I am currently running it with Norton set to allow it