Hi CKC, as you've found out, the LiMN batteries are slightly shorter than the protected ones, hence the need to remove some washers to use the protected ones in the ICON for example.
The protected ones are a little bit longer due to the protection circuit - which isn't needed in LiMN chemistry batteries since they do not vent with flame. I would advise that all users periodically check the voltage of all of their batteries before and after charging and using to be aware of what's going on with them, but it's particularly vital to ensure that the LiMN ones aren't over-charged as they are of a lower resistance internally and this can mean they are more at risk of over-charging than standard protected li-ions.
Hope that helps answer anything you didn't already find on the site and for anyone else that's looking. I think that's part of the reason my forum isn't one of the busier ones, I tend to try to answer all the potential questions right there on the stock listings whenever possible.
Oh and I forgot to mention why someone would want to use one rather than the other. The LiMN are a much higher rated battery, capable of a much greater current draw (8C on the LiMNcompared to 2C on the protected li-ion) which is noticible by some people on some atomisers. Unfortunately, we lose some capacity with this extra draw, but I believe it's a worthwhile trade. Many people just prefer to use circuit protected batteries and if that suits their needs, that's fine too.
AW LiFePO4 CR123A (pair)
AW Protected 18650 
AW Protected 17670
AW Protected 14500
AW IMR18650
AW IMR18500
AW IMR14500
