I'll give a paying player's perspective.
I've been using Start Playing for a few years. I've used the Roll20 find-a-game site even longer, for both free and paid games. My work and travel schedule has made it impossible to commit to an in-person game. Even for online games, I can't commit to being a player in an ongoing campaign. Paid games have been the best way for me to find one-shots, at a time that works for me, with GMs and players I enjoy playing with. And I can usually find a good game on very short notice, especially at Start Playing.
Free games are more difficult, because most DMs running games for free on find-a-game services are looking for players who can commit to a campaign on a regular schedule. As for free one-shot, pick-up games, they are hit or miss. Some are GMs who are into a less-popular system and are just using it as a way to recruit players and it feels more like a performance interview than just enjoying a one-shot game. I've had more awkward personalities (both DMs and players) with random free one shots and both DMs and players are more flaky with free one shots, leading to games being cancelled at the last minute, not starting on time, etc.
My best experiences with one shots are those that are run by people who are (for lack of a better word) "evangelists" for lesser known systems. Some game companies (DCC comes to mind) have their staff regularly run free one-shots to introduce people to their systems and these sessions tend to be a lot of fun.
But if I want to play a one shot of a more popular system, Start Playing is a great resource. If I find myself in a hotel on a friday night with nothing to do, I can almost always find a one-shot that looks interesting. Start Playing makes it easy to filter by date and time, game system, DM play style (self-reported), number of games the DM has run, and player reviews for the DM. I have, surprisingly, never had a bad experience and have never regretting spending the USD 20-50 for a 4-6 hour game.
It is also a good way to familiarize myself with systems that I am thinking of running. Some professional GMs, however, get a little touchy about this, especially if I start asking about how they've configured certain aspects of their VTT setup.
Before 2019, before my job change, when I was running games in person and didn't have a crazy travel schedule, I still didn't have time to both run my campaign for my friends and play regularly in another campaign. Other than some games with old friends over the Christmas break, the only time I played was at a convention I went to each year. The amount I spent at the convention was less than I would have spent if I payed a GM for a year's worth of weekly 4-hour sessions. I mean, I guess there are other things conventions offer, but nothing I'm interested in. I go there to play. That and to browse merchant stalls (which inevitably leads to spending more money, because I'm a terrible impulse buyer at game conventions).
Instead of going to a convention, I can spread out my play time and costs, to play one-shots in a variety of systems over the year. I mean, if one can't afford it, they can't afford it. For me it is paying and playing through Start Playing rather than going to a convention. Also, as I'm not GMing my own campaign in person any more, I've stopped buying terrain, minis, and other physical game aids years ago. Even with regular use of Start Playing, I'm paying less on the hobby than I did before 2020 and it is much more convenient.
