In what situations are foot grills a better option over other matting types?

Foot grills placed outside entranceways help to scrape dirt and debris from shoes reducing what gets tracked into the facility. This can help reduce cleaning and maintenance costs. Whatever you stop at the door, won’t get to your floor. They are particularly useful when the facility is in an environment that has dirt or gravel in adjacent spaces to your entrance ways. This is especially true if you are also in a geographic area that sees a lot of rain, snow, or ice, which all produce mud that needs scraping.
  — Daniel Silver, Vice President of Product Development, New Pig, Corp.

An architect typically designs foot grills during the construction process, as most facility managers will not dig into their floor to create a recessed well. Although grills can be effective in capturing liquids, there needs to be some scraping of the shoe surface to remove the dirt as well. For facilities using foot grills, we often recommend having a matting system in place immediately in front of and after the grills.
  — Aaron Mills, Marketing Manager, 3M Commercial Solutions Division

Foot grilles are a better option over other matting when it is the first of a 2 or 3 part entrance system.  It is also a better option when replacing recessed area grill that has become damaged or ineffective.
  — JoAnn Durette, Vice President of Marketing, Mats, Inc.

In my opinion carpet tiles or matting tiles will provide a better solution in these type areas. My experience has shown that very rarely will the cleaning team of a facility clean underneath where the collected soil is contained. This alone causes IAQ (Indoor Air Quality) issues. Also, I find the foot grills to have a less effective soil and moisture removal surface that can in some cases be slippery if all metal. The metal can be susceptible to undetected edging and or connections being bent that result in possible trip hazards.
  — Mark Roberts, National Accounts Specialist, The Andersen Company

I do not like aluminum and stainless steel foot grills.  The only time they are a better option is when money is no object and the architect or designer cares more about how something looks than how it functions.  
  — Mitchell Saltzman, President, Proform