I totally agree with you. But checking the polarity and finding its the wrong way round is one thing.. You then need to swap it back to normal.I would always use a tester, even in the uk never mind abroad.
I have never had a problem in the uk but better safe than sorry.
Using mains electric with reversed polarity is not safe.
A tester will only cost £6-10 pounds and it takes seconds to plug it in and check.
Socket Tester Mains Fault Checker Display Digital UK Plug Malfunction Detector x | eBay
1 x Switch Detector. Automatically detect sensitivity, used for power socket wiring detection and RCD testing. Professional circuit design, stable performance, simple test. Due to the difference between different monitors, the picture may not reflect the actual color of the item.www.ebay.co.uk
I have the same tester. Works very well and having the voltage info as well is a bonusI would always use a tester, even in the uk never mind abroad.
I have never had a problem in the uk but better safe than sorry.
Using mains electric with reversed polarity is not safe.
A tester will only cost £6-10 pounds and it takes seconds to plug it in and check.
Socket Tester Mains Fault Checker Display Digital UK Plug Malfunction Detector x | eBay
1 x Switch Detector. Automatically detect sensitivity, used for power socket wiring detection and RCD testing. Professional circuit design, stable performance, simple test. Due to the difference between different monitors, the picture may not reflect the actual color of the item.www.ebay.co.uk
Just a note. The little short leads to swap the L and N to get the polarity back again are very handy. But .... It is not something you should actually be able to buy as you are being provided with an electrical product that has been deliberately miswired and would of course fail any kind of PAT testing or similar (the fact it is being provided to correct a miswiring doesn't matter - two wrongs are not meant to make a right).
The problem is you have too fancy a piece of kit. Us normal plebs carry the cable around coiled and tied with a bit of string.
The prices of that kit lead set in your link is pretty good I have to sayI don't blame you in this "sue it society" However, there are loads of these polarity reverse leads kits for sale. Not sure if they need a PAT test as they are not an electrical "appliance" .. a gray area.
Your crossover switch is brilliant but think I will stick to the leads..
Carry the EHU cable around in a plastic bag if you like
most EHU leads are "loose" anyway and not on reel-out spools like the 240v extensions we all use nowadays. 
Better to have a long cable than 2 short ones as often they are driven over and plugs don,t stand up to well to that and for that reason better cheap than expensive cable
This is much more handy.
similar(ish), at one of my sites we had all these smart LED lights fitted, looked good but unfortunately they would all do a really quick flicker at the same time, no pattern to it at all and quite a lot of time was used up fault finding. Then a bright spark (fully intended pun) clocked that it happened when the lift motor engaged, micro second of volt drop was not noticeable on the fluorescents, just the LED's. Was never resolved but some things just aren't worth the botherNot really that relevant for mains cable but while it is in my head ... If you have any data/signal cables (long network cables, TV Aerial cables, etc) then rather then coil them up for tidiness, go "to and fro" with them so they are not round and round. That avoids any interference on the cable (I remember that from a job many decades ago when troubleshoooting a printer that would randomly print corrupted characters and couldn't suss it for ages. Traced the cable route and under a floorboard by a lift was metres and metres of printer casble coiled up next to the lift power cable. Everytime the printer was running AND the lift was being used, printer printed rubbish. Relaid the cable to get rid of the coil - fixed the problem
