On ebay bog standard chinese can be what ever. Usually all promises of accuracy are purely fictous along materials, hardness. etc. Some are really appaling low in quality.
As said on chinece the ones sold by CTC and ARC are much better in general.
If you need real tools and not just tool shaped objects I can recommend LAIP, Spanish comppany and stuff I have bought there has been made in europe. Least 6 years ago it was.https://www.laip.es/
There was a tool shop in this village and they ordered the stuff from the catalog and I got allways the stuff in a week or two, I did need to pay catalog prices, but there were no surcharges or such. Bough Ortlieb collets and such. Not really that much more than chinese/indians if you find a place where they sell these.
Then there is price....normal good quality ER40 collets cost about 16 EUR/pcs and you get brand name, brand precison. Ultra accurate (relative in ER collets I don't see much use in our world) REGO-FIX 1140.23001 DIN 6499-B are about 40 EUR/Pcs.
Would German made standard collets be good enough? One option would be Fahrion.
Engineering Supplies.co.uk, but ask Simon first. Looks like he is limited to ER32http://www.engineeringsupplies.co.uk/tool-holding-collets-c-171.html?menu=1
ER32 brand name collets would be about 13 GBP a piece:
ER32 Collets (6 micron) Fahrionhttp://www.engineeringsupplies.co.uk/14mm-15mm-er32-collets-micron-fahrion-p-6707.html
I'm geting few collets for "testing" there. I'm trusting more on rigidy than utmost accuracy. How good the spindle can be?
R8 is a pretty small...do you really need ER40? Nut tightening is to about 170 Nm.
my few eurocents...