MY department just bout 24 of these viking z-sevens there a great pack.. these were replacement packs. prior to purchasing these we used the ISI viking Dx model. The only down fall of these packs it take 17 AA batteries. But i have recently discovered that ISI has a upgrade to the pack to out fit it with C4 upgrade . The C4 upgrade allows the pack to run all the bells and whistles with 4 c cell batteries instead of the 17 AA it requires now ... but other than that a great pack...