The Park CT-5 is a great option for the average cyclist. It's a comfortable, durable chain tool for a very affordable price that fits the majority of bike chains (from 8-speed up to 11-speed), but won't work on the very specific Campagnolo chains.
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Pros
Pro Everything you need in a chain tool for an affordable price
The Park CT-5 will fit almost any chain an average cyclist will encounter, from 8-speed up to 11-speed. It's maneuverable, surprisingly comfortable to use, and light enough to carry with you for emergencies.
Pro Maneuverable
There's an idea that inserting the pin from the frame side of the chain will make the link stronger. The CT-5 is small and light enough for you to be able to do just that.
Pro Fits most chains
The CT-5 is suitable with chain sizes from 8-speed up o 11-speed, for every brand except Campagnolo parts (which isn't unusual, since nearly all Campagnolo parts are non-standard).
Pro Doesn't take up a lot of space
The CT-5 weighs only about 78 grams, so it's both light and small enough to easily fit into your bag to take with you, to be used in case of emergency.
Pro Comfortable to use
The crank on this chain tool doesn't dig into your hand when you apply some force to it, which you always will when changing your chain.
Cons
Con Not suitable for Campagnolo parts
If you're planning to work on any and all bikes you might encounter Campagnolos (or "campys"). Their chains are non standard, and this tool isn't won't fit them.