The .75 is not 75% worn per se.
A chain checker measures chain stretch.
Chain stretch is an indicator or wear-and-tear.
Parts of a drive train wear at different rates. For instance the teeth of the chainset will show wear when they become "shark-finned". But this could be long after the point at which you should replace a worn chain.
If you persist in using a worn chain - though you may not notice anything detrimental - but when the chain eventually gives up - and you put a new chain on - you may find it skipping under load through the gears. This requires replacement of chain-rings / cassettes.
An earlier replacement sought - would have prolonged the life of chain-rings / cassettes.

As for your last question - it is difficult to say - if you ask a manufacturer - they will say no difference. Personally, I think the wider chains lasted longer and are stronger than the narrower 10/11 speed chains of today.

Don't know of any exceptional single-speed chains ... just keep it well oiled and it will last longer.

What does chain worn indicators 75% mean?
Mbo_Form - created object. Mbo_Form  it is written on VF on the custom controller.
As clicking on the tab or by clicking on Mbo_Form record this tab, redirect when loading a standard page on the custom page?
