Most ESR meters are not meant to be used in circuit, as there can be parallel low resistance paths that give an erroneous pass indication. However generally if you use it in circuit it will in most cases be somewhat reliable in showing faulty, but the one linked is not exactly great for ESR, only giving a pass fail reading, and the ESR of most capacitors really is low, and the line between working and fail is very small for low ESR capacitors, typically well under 0.5 ohm is reasonable, over 1 ohm is generally a fail, and this one has a pass fail resistance of around 5R.
will work for most general purpose non low ESR capacitors, and for pretty much all high voltage capacitors which in most cases have a high ESR, but for low voltage and SMPS electrolytics it will only show you grossly failed capacitors, not those on the way out only.
You probably want one with a scale showing you the ESR in ohms instead.