I don't know about how it works in the UK, but in many parts of the US, certainly California, it's also an objectively bad deal.
If there is a stated amount of vacation time in your contract, the company has to pay out full salary for any vacation time you don't take, at the time of departure. Vacation is good, people should take it, but the incentive structure of "unlimited vacation" is skewed towards less actual vacation, and no compensation for that choice in the event.
If someone offers unlimited vacation, take them up on it! But make sure that the contract says "four weeks guaranteed, plus whatever other time you want". If it's unlimited, then it should be the same deal, right? This is also a good way to gauge if the unlimited vacation comp is going to be undermined by pressuring workers to stay on the job.
About the pressure part that is also totally true. I don’t think “unlimited” is possible at most companies. It has to be part of the culture. That is why I find it important to encourage people to take holidays and do so lavishly myself. It also isn’t so much unlimited as much as we simply don’t keep track. It wouldn’t be ok in most cases to take 2 months in a row, although it has happened. Also, we work in shapeup cycles and usually prefer people to not take last minute holiday within a project.
As I said this is all pretty vague and yet it is amazing for everyone who works here.
I do hiring on the engineering team and in this case it really works against us because it simply is too vague. It has a high “trust me it’s cool” character that a specific number would fix. “50 days” sounds more clear.
You really need clarity on how much time is allowed so you can calculate how much are you making per hour spent in that company. In the end I was taking all the holidays who were mandatory in the country I was living and no more - and people were really pissed off.
American people were taking zero holidays to show they were "committed to the company". I know some people had conflicts over taking too much holidays.
Overall, you end up with people at the extremes doing too well or too bad and average people being more on the bad side than on the good one, trying to impress their managers.
Where I work we don’t count holidays and I encourage all my reports to take full advantage. I’ve been on holiday twice (2 and 4 weeks) this year and take off a week here and there and I never have to worry about what I am going to do around Christmas, I always take another 2-3 weeks then.
But since “don’t count them” is a tad to vague for many people, just go for a high number like 50