The clearcoat inks from all of the manufacturers, whether they be called "chroma" or "gloss" "optimizers" or "enhancers", all seem to be engineered for optimal results on RC photo media, and RC media are what the marketing folks show you at trade shows. Deviate from RC media, and none of the current printer clearcoat options work as well on non RC fine art Glossy/luster type papers. They aren't laid down thick enough to do the job expected of them. As such, for those of us who print on non RC papers, the clearcoat inks offered by any printer OEM represent only a partial solution to the problems of differential gloss and bronzing. I've even gone so far as to send a print sample through a second printer pass (tricking the printer to run the clearcoat totally across the entire print surface again by sending a perfectly white (rgb = 255, 255, 255) "image" to the printer driver on the second pass. That approach can work quite well, IMHO, but involves a second pass through the printer which is not an ideal answer.
If you are of the opinion that viewing a print under glazing and when looking perfectly normal to the print surface suppresses all gloss differential, bronzing, and even surface texture features of the media you have chosen, then you probably shouldn't even care about clearcoat features nor own a printer that has a clearcoat channel, and all of this discussion gets rather academic very quickly. If, on the other hand, you anticipate that some people will observe your prints at angles other than perfectly perpendicular to the print surface, or perhaps even view "naked" prints not placed behind any glazing or laminate, then gloss differential, bronzing, and surface texture features are all factors to care about when their presence is disagreeable to you. The best clearcoat performance I've seen to date actually resides in the prosumer Epson SC P400 desktop printer model, but that gloss optimizer technology is not available on any of Epson's pro/wide format models. An equally competent clearcoat performance was achieved by HP on its venerable Z series printers, with the enduser being able to increase clearcoat thickness by customizable preset media settings such that the gloss enhancer works pretty well (but not perfectly) even on non RC fine art glossy/luster media. Canon's chroma optimizer is probably called "chroma" rather than "gloss" for a reason, because as Scott Martin noted, it comes up short as a total clearcoat strategy, particularly on non RC media.
IMHO, there's room for more improvement with printer clearcoat technology among all of the big three printer makers, and even today, if differential gloss and bronzing issues are to be totally eliminated on gloss/luster media printed on with pigmented ink printers, one still needs to resort to post processing spray coats with products like PremierArt Print Shield, Hahnemuhle Protective Spray, etc.
best,
Mark
http://www.aardenburg-imaging.com