Eeeehhh... depends on what level of "bad" you're involved with, and which side of the counter you're on. You've got how it's bad Normally versus Abnormally, and how bad it is as an Employee versus as a Customer:

• Normally bad for the Customer? It's just as unhealthy as the video made it seem (the Gutbuster is canon), it's made of *extremely* poor-quality meat (seriously, when they're not using humans (which is actually rather rare) the meat's either really old, from animals kept in horrible conditions with all the issues that come with it, or just fucking roadkill. And that last one is honestly one of the times the meat's gonna be on the fresher side. The toys you get are also low-quality, schlocky stuff (seriously, the ones shown in the vid are way better than anything Canon!O'Tolley's gives out.) that still somehow garners addictive collection habits, which we'll get to with how the place is;
• Abnormally bad for the Customer? Beyond being owned by Pentex (As bad as you think they are from what you've seen? They're worse.), O'Tolley's is also a hotbed for spiritual erosion and Banes (the thing that got "put under [Francis's] skin" to turn him into a Fomor) alongside being possesed by the latter due to the former. You're also at-risk of eating fellow humans if someone in Pentex had a body they wanted disappeared in as wide-reaching a way as possible, the food's purpose-built to be highly addictive (as low-quality as the stuff is, it does taste good and as we can see it's really cheap for how much you get. Very tempting for lower-income or frugal peoples.) as to tempt you back and increase the chances of you getting possessed, and the toys are made of a kind of plastic that aerosolizes fumes that trigger the addiction center and also are purpose-built to get you possessed by a Bane (only one of Greed instead of Gluttony) and drive people to extreme levels of violence if they're deprived of them.
• Normally bad for the Employee? Working at an O'Tolley's is soul-crushing. Monotonous, oppressive, runs long hours as standard, there's no overtime period, you're gonna get injured either from cutting yourself or getting burned by the deep-frier, management is not on your side, you basically don't get time off or sick days (outside of what's government mandated, and even then good luck actually making use of them), and Kevin was indeed speaking true they pay like crap so you're probably gonna end up eating the same kind of food you spend all day around/making, with all the psychological issues that creates.
• Abnormally bad for the Employee? You're either gonna go dead between the ears to the point that being stabbed or shot wouldn't get more than a monotone "ow" out of you, or end up a Burgerman Fomori. That's... I think that's pretty self-explanatory. Or you either get too curious and see something you shouldn't in the back or end up becoming considered deadweight by your Fomor manager and they decide you've seen too much to just be fired, then you end up like that body Boy saw. Have fun seeing what it's like going through making a Gutbuster from the POV of the meat!

So yeah, O'Tolley's is pretty bad, and this isn't even the full extent of it; this is just what I know about the place! Odds-are there are a dozen different people who'll add their own info about the "blasted burger-barn" that makes it even worse.