Dunno about 'indie', but it's free, so what do you care?
Yes, this is legal. Both the company that originally created the game for the PS1 and the company that bought them out went bust, so the game was placed under a GPU license, allowing modders / porters to use the sourcecode to make a PC game of it.
Yes, it works too. It actually works a bit better than the original PS1 version, IMO. If it's giving you glitches, either you haven't downloaded both of the files you need, or the server shat itself halfway through one of said downloads. Try again; 9 times out of 10, re-downloading it will fix bugs.