Just so there are no mistakes or mishaps "in circuit testing" is with the mains power sources removed and the circuit deenergized. But "live or energized in circuit testing" is a totally different approach and set of tools.
As mentioned above by Specmaster, in circuit testing is not going to work in ALL situations. But it works in MANY situations, once you have a suspect component it pays to also test it out of circuit as well, which is done by lifting a leg or completely removing it.
For in circuit testing you need a multimeter with diode, ohms and I suggest capacitance. An ESR meter for electrolytic capacitors is very useful, and almost essential as a repair tool. ESR is just an easy way to characterize aging/failing/defective electrolytic capacitors.
Instead of the Peak Atlas for ESR I recommend a Bob Parker inspired design. Main reasons being that it's repaired easily, schematics available, large display and input voltage protection (past 50V if the version purchased has diodes added).
The Peak Atlas only good for 50V input protection, it does have the extra discharging and capacitance measurement features however. Why is it still a bad choice? You should be discharging all capacitors manually yourself for in circuit testing out of habit. You will eventually forget or miss a cap and at that point you want as much input protection as possible to take the brunt of any damage.
Personally I would stick to capacitance on a multimeter there should be a lot more protection from mishaps and you can check voltages before taking a capacitance measurement. For out of circuit testing (as it has no input protection) the DER EE DE5000 is the handheld instrument of choice for inductors, resistors and capacitors. The tester you linked is still valuable as a cheap analyzer for semiconductors or as an interim step to getting a DE5000 (again no input protection).
Currently there are three manufacturers of the Bob Parker design.
- Evb who sells several different models so look for the model with protection diodes.
- Altronics k2574 which is only in kit form, you need to add the diodes yourself.
- Anatek Blue ESR Meter has a slim case so limited options for adding the diode protection internally. You can buy the kitset or the assembled version.
https://evbesrmeter.pt/https://www.altronics.com.au/p/k2574-esr-meter-kit/Bob Parkers website
http://bobparker.net.au/esr_meter/esrmeter.htmIf you make the Altronics kitset read this page for diode protection
http://bobparker.net.au/esr_meter/esrhints.htmSo in summary a good safe multimeter with capacitance (handy). Bob Parker designed ESR meter with diodes added, a cheap component tester and DE5000 will give you a complete enough set of tools to cover most in an out of circuit testing (without going too crazy).