Considering this is a new one on me, I doubt many people have even heard of them yet (which explains the thunderous silence.)
However, I honestly don't see the utility. If you use the proper oil (API Service SL or earlier,) you should not have trouble with flat tappets. If you use API Service SM or later ("Energy Saving," typically with no accompanying Diesel rating) the extra oil won't help (it's not the oil proper that wipes out cam lobes - the base stock doesn't change. It's what's added
to the oil that makes it different.)
Ideally, roller cams for "vintage" engines (specifically referring to AMC Gen-II/III V8 and AMC I6 here - since they're most commonly overhauled...) and tappets would become available for prices comparable to SBC/SBF/LA-block. But, the economics of scale prevent that.
I have heard of "composite-foot" tappets that are supposed to obviate the need for elevated organometallic antiscuff additives, but I have yet to gather any reports from the field.
Myself, I've always preferred Rhoads tappets for performance buildups - but they have "flat" feet as well (a "flat" tappet is not truly flat - there is a radius to the foot, typically 30-36". This works in conjunction with a slight lateral taper on the cam lobe to rotate the tappet in the bore, which helps to reduce wear.)
(Generally, when your post hasn't been answered, it's for one of two reasons: 1) No-one who has an answer has seen it yet. 2) No-one has an answer. It is generally not
necessary to "bump" your post hoping for an answer, and widespread use of "bumping" can lead to increased server traffic and load. Besides, it's "bad Netiquette," most places... Just sayin'.