don't use electricity is best

/k trolls aside, the post is correct just the context is incomplete, click the link

user is converting 3 pin to 2 pin without the grounds, some things are only 'live' switched, so on a 2 pin if reversed, it will become 'neutral' switched so the live goes all over the electrical thing and can leak around but not enough to trigger a ground trip

is there any small tool (like a plug) than I can use to check?

use this?

Many people may get confused when even the AC plug has polarity.

Two pin plug as shown by you has no polarity but some AC plug especially the blade type has polarity indeed.

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By polarity, it is not talking about Voltage/current polarity but just connection polarity. As you know AC voltage has no polarity. The switch suppose cut off power on L side, not the N side. So, the plug with polarity will ensure that the L goes to the switch. If switch cut the N side, it means the opened L side which still has AC current in it still go through device/appliance before being cut off at the switch on the N side. Therefore the AC current still exist in the device/appliance.

The description above is not really related to your case though  You can hear or read advise somewhere that if your appliance has some sort of electricity shock to the body, you just need to rotate plug and the tingling shock would be gone or at least reduce. This happened to appliance with power supply transformer inside to reduce operating voltage.

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Some appliance has chassis connected to the N of transformer secondary. By this I meant the top side of transformer is L and the bottom side is N. If you change the polarity of the AC plug,m the secondary voltage on transformer will be out of phase to the AC on primary. Thus this will increase the tingling sensation compares to when the AC between the primary and secondary is in phase. However, in both case, it is still safe because the "touch current" should be in compliance with UL or IEC standard which is not more than 3mA current limit.