I had never heard of them before either until I had to buy a new PS unit last week.
I read where if you have an OE unit and it has never been replaced, if it does not have one then there is no need to add one. But, If you have to replace your PS unit it is recommended by "some" of the manufactures to add an inline filter with the new/re-manufactured unit.
I checked four online sources for my PS unit and all four suggested an inline filter in the description of the pump.
I did purchase the above filter and I installed the PS unit and filter over the weekend. The filter makes sense and it can be taken apart and cleaned.
I still wonder if it is due to the manufacturers not running clean fluid thru the pump during tests which would suggest "floaters" inside of the unit when you buy it from the parts store. This may be their way of cutting down on receiving as many returns from customers.

Thanks for the replies.