Some people hate cover cloths but I like them. I prefer them to using a dummy board or a part filled frame because I can, if necessary, just roll it over the top of the box and walk away. Handy for covering supers too, temporarily.
Don't be tempted to buy them, especially the ones with a hole in the middle - they're useless in practice. Easy enough to make from any bits of fabric larger than the top of the brood box (pillow case, tea towel?) just make a channel at each end for a bit of batten to weigh the ends down. Slide it out for laundering. All my cloths get washed after use, just shoved in the washing machine with the suit and gloves.
Disease transfer isn't really an issue within a single small apiary, because bees often drift from one hive to another anyway. If either fb is suspected then the whole apiary is on lockdown anyway, not just the suspect colony, and all kit should be cleaned - including footwear - just in case. Nothing out to another apiary until the colony or colonies have been checked by SBI.
If you have more than one apiary you'd need to use clean cloths for each site. Some people keep a set of kit (smoker, hive tool, gloves etc) for each apiary, as well as a fresh bucket of washing soda.
