I've got the same model xc90 (185bhp) and purchased a BSR tuner about 9 months ago. I've done around 8000 since and have had no problems. The car is more responsive but it's had no effects (positive) on fuel economy. I went for the BSR tuner because you're able to put it back to normal any time you like - I didn't like the idea of being reliant on a garage to put it back for me.