Getting random people from the internet to 'test for free' is a pretty risky and frequently terrible approach to testing, especially at when you're in actual alpha builds.
One of the biggest hurdles in alpha testing is being able to see beyond what is currently there, and visualize your way through the software that could eventually be there. This will also frequently include visualizing multiple options of what could be there, how different features could potentially function, and weighing these options against each other before attempting to proceed down any given road. If you are dealing with alpha build software then you need to have very close control over who is using it, how they're interacting with it, and how well they understand what is actually going on at that stage of software development.
It is however a sad truth about the industry that testing stages are all too often under valued or completely overlooked during development. Testers are frequently under invested in, used as a screening or entry level position while paying as little as legally possible for it, and commonly allowing staff to 'advance up' from the 'lowly noob work' of testing rather than fostering comprehensive and talented test teams who can tell their own backside from a hole in the ground as far as testing in software development goes. Skimping on QA, especially early on in projects, is kind of a fool's economy due to the risk of bug snowballing effect - The worse the state of the code base, the harder it is to work with, and the longer bugs go on for the harder they are to fix completely. The harder it is to work with the slower the progress on future development is. The slower the progress the more stress coders come under, and the more stressed coders are, which translates into increase likelihood of burnout and turn over. Turn over then translates into even less comprehensive understanding of the project, which compounds the problem of fixing bugs and making progress, and that then risks making the cycle roll over that much faster.
Over my years in the industry I have seen several multi-million dollar projects in different fields get caught in such death spirals for the want of saving an extra $60-100k a year to put towards additional testing and oversight. "Saving money" on QA is often one of the most expensive choices companies make, and I rather doubt that is going to change any time soon.