Once a casino promote themselves to be VPN friendly, there is no need to worry about using VPN. If they blame us or make a story up later due to the use of VPN while in fact we do not do something against the other terms, the casino should be responsible for it. Coming to mirror link, yes it is useful for those who have an issue with ISP but it may not work forever because once the ISP aware about the mirror links, it will all be blocked so players will need to wait for the casino to create new mirror links.
VPN usage is usually a tricky affair which involves a lot of variables which is why it's best to do proper research before deciding whether to use them or not. Same logic applies to mirror links too.
Generally, it's always best to consult with the site's customer care and maybe even save their responses before deciding to use a VPN or mirror link in my experience.
As far as I know Shuffle is VPN friendly casino so We can assume that its safe to use that as long as they are in allowed region and don't have any intention to violate something on their casino.
But if they are in restricted region I guess people should think automatically that its better for them not to use VPN since for sure that they would really get a problem for trying to bypass the restriction.
I agree with you that always the best action to do is to contact their costumer support since they would never get any wrong answer from them. Then also for sure that they can get good advice about what better things to do with their plan to use VPN in their casino.