I absolutely love these things, the folks at one drop really had their thinking cap on when they came up with this idea. Obviously, being able to change the color and shape to customize the look of your yoyo is cool. However, being able to change the weight of your yoyo so that it feels closer to how you want it to feel his outstanding. I don't find that the change in feel actually affects the play much, but I do find it surprising how different a shift from the ultralights to the heavier flat caps can feel. Also, I probably play my one drop yoyos with side effects more than any of my other yo-yos simply because I know I can switch the axle system out if I somehow damage it. My kids yoyo as well and we have experienced a couple stripped axle hubs in my household (although never on a yoyo with side effects); and it's awfully hard to stomach stripped threads and then your yoyo is toast when one drop throws are sitting on my shelf and have figured out the solution. I unscrew my one drop yo-yos with impunity whereas I'm a lot more careful to laboriously pick knots out of my other throws.

Really the only negative here is the cost. I'm surprised how expensive these little suckers are, but they are a lot cheaper than having to buy a brand new yoyo if you strip out the hub. Make sure to research the weight of a given shape and material of a side effect before you buy it, so you don't end up with an unexpected change in feel.

I love side effects. They’re fantastic. They’re a quick and easy way to add character, personalize and fine tune your throw to really make it your own. Day one, I loved side effects. I love that they’re easy to replace, they’re durable, they look good and if you strip these somehow, unlike with other yo-yos, you just slap new side effects in! A no brainer for your trusty One Drops. Always good to have a few around for when you need them. For One Drop Side Effect compatible yo-yos of course. Might not be a good idea for any other throws.

Pretty dope