When it works it works very nice but if you have troubles with Argyrotype just leave it aside and go for Vandyke. Just pay attention to the following:
* Rinse the print at least 2 minutes (total) in two successive baths of 1% citric acid to eliminate all unreacted iron ions. Only then use tap water. (That you're certain is not alkaline and doesn't contain iron impurities!) Do not reuse the citric acid first baths, mix fresh for each print. (You don't have to be exact; weight as kitchen recipe such as say... 1 teaspoon per 1000ml...)
* Always tone your Vandykes with gold, platinum or palladium before fixing.
* Do not overfix; 2 minutes in 2% plain anhydrous sodium thiosulfate is more than enough. (Refresh fixer often though! For instance, I don't use the same fixer for more than 3 prints...)
* Wash thoroughly.
That's it, no need to complicate things more than you need to. I like the idea, but I won't do Argyrotypes again -> I'm convinced prints processed as above are as achival as (if not more!) any well done Argyrotype...