Well, okay, it is speculating, but not for the sake of speculating, just to save on travel.
It’s also a saving pot in a way - you put money as EUR and it’s there until you spend it. You won’t take money out because it will cost you to get GBP back. 
As part of holiday prep, I research currency. For 3 trips (out of 4, I’m only looking at higher spend trips, not 3 days in Prague), I would save money if I exchanged it at the time when I was checking. When you are planning 4 weeks, it can really add up.
As a whole, Revolut doesn’t give me anything better than Monzo apart from prepurchasing currency. With Revolut I COULD buy EUR now, while Monzo won’t give me this option. That’s only difference - it allows me to risk on currency exchange and potentially save money. If Monzo would offer this, I would definitely consider going from assumptions to trying it out for real.
I don’t think it’s enough to make me want to get in bed with Revolut. 
To be really objective, I was usually looking at crappy rates, that was before I met Monzo and got educated by fellow Monzonauts
. It seemed I could really save a lot more money, because buy/sell difference was more substantial. I’m going to re-evalutate if I still fancy this idea after trip to Morocco (end of April), EUR rates are in the previous post. 