I've been using mine daily for almost two years now and it's totally paid off for me. The biggest advantage honestly isn't even saving oil (though that's obviously nice), but that I can get food on the table way faster. When I come back from the gym and want to eat something quick, fries or chicken pieces are done in 12-15 minutes. With a regular deep fryer that takes longer and the prep is more annoying.
About the cost: yeah, 80-150€ isn't nothing, but if you really fry stuff regularly, it pays for itself. At my place with two kids we probably go through 5-10L of oil a month, so that adds up. The trick that a lot of people miss: don't cram too much in at once! If you pack the basket too tight, it'll fry unevenly. Better to do two batches, especially with bigger stuff.
But let's be real, if you only fry like 1-2 times a month, you don't really need this. Then it's actually a waste of money. Think about how often you'd actually do it. And about brands: I got a cheaper Cosori one and not the Philips like your mom has, but it works just as well. The big brands don't have as much difference as people think.