I used to use dumbbells with collars so I could change plates and various weights as needed. The two problems with the collar type dumbbells are the time it takes to change weight and the bulky nature of the bar that sticks out either side. The time problem was never much of an issue for me, since you are supposed to be resting in between sets anyhow. However, the portions of the bar that stuck out started to bother me, after I read that this bothered someone else. Thus, I invested in some hex dumbbells, but only when I could get them on sale or with a coupon or something. Don't talk about those smart dumbbells (great oxymoron) that adjust on the fly; they look like silly and are uber expensive. Of course, to buy a complete set of hex would be less than the adjustable, but that is so far-sighted. I wonder when free weights got their name. It is not like there were machines at first that had the name bound weights. Shouldn't they just be weights?