NaNoWriMo is great. There’s a great support group and doing it with other writers can be great motivation, and if you really want to get out a first draft, that’s awesome.
Agents say they dread NaNo because there are people out there who write their 50K word draft and then query it immediately. As long as you’re revising and incorporating feedback from crit partners and then polishing up you have nothing to fear.
However, thousands of people do NaNo, it’s not necessarily something to put in your query. (You can however, totally put their certificate on your site).