Having investors changes the equation quite a bit. Depending on how much they've put in, that should give you a good runway to be able to experiment with the pricing model. Wish you the best of luck!
I admire the intentions and the hard work behind this however...
The issue I have with pay-what-you-want or low revenue business models is they're unsustainable.
Either declare something a passion/charity project and make it complete free (but perhaps open to receiving donations) to properly set users' expectations or monetize it.
I takes a lot of time to develop and maintain complex technology like trading tools.
I don't know what the founder's background is. However, if he makes good money from other sources, after the initial euphoria of sharing his tools with the world goes away, he'll have stay motivated doing the grunt work to maintain it. And pay out of pocket for expenses and the value of his own time a PWYC pricing model likely won't cover.
Making money (and a profit) isn't evil or bad, it's necessary both to see if your market (and audience) deems your product worth developing and to keep yourself motivated (and compensated fairly enough) to work on something.
A lot of companies have shut down due to lack of funds (or the ability of makers to go without making much money). It's risky for an user to try a product with a tenuous future, come to base their work flow on it only for it to be closed down down the road. Especially with something like trading.
Having investors changes the equation quite a bit. Depending on how much they've put in, that should give you a good runway to be able to experiment with the pricing model. Wish you the best of luck!