I've used them with mixed success, same shop, different results.
I went to buy workwear for a new job, it was really worthwhile, got lots of stuff I wouldn't have tried, there wasn't any pressure to buy more than I wanted, but to be fair it was clear I would be buying something.
I tried it for jeans. Sadly they knew naff all about jeans and I bought an expensive pair that had to go to charity.
I went to buy a party-frock that I could wear for a special occasion and thereafter to a casual wedding. Wild success. They found me a fantastic frock in a brand I'd have simply walked past, it was totally out of my comfort zone and I love it to bits and wear it whenever I can get away with it.
I tried it again for another special occasion. A bit more ho-hum, not sure I even bought anything.
I think you need some sort of brief for them to work with, and in a department store with different brands you need to be prepared to say what sort of price think is reasonable. In my experience I felt less pressure than I would feel in a more casual thing where an assistant starts trailing around a shop after you suggesting thing. I'd say worth a try.