Static dissipative ESD footware
I've never seen such things advertised before BUT I have every reason to think they are serious. The site in questi0n sells shows signs of having been there for at least 2 years and they sell only anti ESD footware. A good first indication of credibility.

In many cases search engine results for a selected product start to turn up garbage and unrelated results in many cases after the first few pages. If you do a
 Gargoyle search for "heel grounders" and then look at the results around the 500th results      

ALL the entries are still specifically about the expected anti-ESD product.
 500 entries for "heel grounders is impressive - assuming they are not padding their results - as may be the case. Chinese sellers of a product tend to advertise many pages and hundreds of instances of a product even when they sell say 5 or 10 actual products. I haven't checked but this may greatly skew the results.   


Real world 


I have visited a range of factories in China - with the bottom end ones having no concept whatsoever re requirements for taking ESD precautions.  But in the  "realest" factories that I visited, where products were manufactured for name brand international electronics giants, all visitors had to don "lab coats" and protective hair covers. Visitors either had to (various locations) add heel grounders to their shoes, or leave their shoes in a rack and wear supplied clean and ESD safe footwear, or to place tasteful shoe enveloping conductive and dirt protective overshoes over their shoes (no part of own shoes touches floor). Some management staff wore apparently conventional shoes but with heel grounders. ALL work trays for carrying components or semi finished products were of ESD safe materials and a significant number of negative ion blowers were in use throughout. Signs summarising ESD safe and other work practices were prominently displayed. ie there is no doubt that they were highly serious about the issue - enough so that it would impact their effective overall productivity if unnecessary in locations where throughput cost high tech $. I've also seen factories where eg COB level manufacturing (blob on board) and LCD assembly where "sensible" protective measures were taken (wrist straps, work surfaces) but with no apparent use of heel grounders or ion blowers.

How real is ESD danger?

When I first saw this question I thought it said something about general opinions in this forum being that ESD protection matters but can be treaed relatively casually. I don't see that remark there now  - it may have been deleted or I may have seen it elsewhere. 

While I myself have commented about ESD protection being oversold by the sellers of protective equipment, it is a very real phenonenom and there is no doubt that damage can happen. I have mentioned here personal experiences of ESD damage happening under under specified conditions and vanishing when problem sources were addressed. Shoes are not the only way to deal with such problems but in an environment were the floor surface was properly controlled they may be cheaper and as effective as wrist straps and similar.