Getting first 100 users: Advertising vs Manual recruitment
I have just completed the private BETA of my product (https://www.concordapp.in/). But the product is still not able to retain the users. So I'm not sure if it is useful to go for acquiring more users via ads or do a second batch of testing.
I would recommend manual recruitment to get at least 10 people to use it, work out the kinks to spot anything that may obviously need changing (its so important to get a pair of eyeballs that aren't yours).
Then when you feel comfortable throw in a small ad budget!