Yes and No.
You have the wrong approach. You can't predict success and you can't predict what markets will work and you can't prredict what the perfect product for a market is. You have to release products and track ALL possible metrics and tweak consistently.
Basically, even the really big companies have hits and misses. And more misses than hits.
So, firstly, you should be releasing 5 or 10 high quality web apps and seeing which stick and focusing on the ones that do.
That's the first step - finding a market demand.
Second is hitting the value for money/quality/perfect market fit.
That's the second step - after you have found market demand, making the most of it.
An inbox cleaner for $20 is just too expensive. Too much friction - especially for a new product from an unknown developer. You have to minimize regret for users - or rather, potential regret.
Instead of thinking in terms of what you want to make think in terms of what people want to get in terms of value for money. 5 people is too small of a data point. So you have to lower the price anyways - to get enough customers to find out whether there is market demand or not and what things people want and what they are willing to pay for.
So play around with the price a bit. Plus release 4-5 other products and see if you find a market with huge demand - one where even lower value for money sells well.