Tom,
The Outlets To Go Power Bars are apparently designed to operate on 220VAC electrical systems, but I had a bit of trouble verifying that as the technical information on the Monster Cables web site was a difficult to find. I did find one reference in the FAQ's section which states:
"Can I use my Outlets To Go in a 220 / 240 volt country?
Yes your Outlets To Go will function with the appropriate plug adapter. Make sure that any devices you will be using can also work in multi voltage applications. If not, a converter will be necessary."
If the product you're using is just a "basic" Power Bar with no Surge Suppression or other features, it should be fine. However, I'd probably still check the "nameplate ratings" for maximum allowable voltage. These should be listed on the unit somewhere, probably the bottom.
I'm not sure that the built-in circuit breaker in a Power Bar designed for 115 VAC would operate properly, given the fact that devices will only be drawing about half the current at 220 VAC. However the outlet should be fused appropriately, so this should take care of any overloads.
If you want a definitive answer, you could send an E-mail to Monster Cables.
Good luck!