alub, I had a lot of the same questions when I started dabbling recently in Vending and Affixing coils. I had assumed the same requirements would apply for authenticity as for government issued coils (including parallel straight sides). However, as noted above by some of the members here much more experienced than I, the production process was different than for "regular" coils. Also, if you explore the certificate databases (such as APEX or Philatelic Foundation), or look at certified examples sold at auction (if you do the free registration for
http://stampauctionnetwork.com, you can do a search for Mailometer in closed [i.e. sold] lots. Many will comment on accompanying certificates), you will find MANY examples have similar irregular sides as those above.
The Belasco book Chris mentions above is well worth the cost. As a general rule, it seems that the regularity of perf hole pacing and the size of the holes correlates more to authenticity for Vending and Affixing coils than other features (at least when it comes to evaluating examples online). The stamps shown above (which I happen to watching on
ebay, as well) seem to be well aligned vertically in the perf rows and have consistent spacing between holes. I think they look legit (my disclaimer: I am new at studying V&A stamps and I do not actually own a certified copy of this type).