Monster is making a push into the sports headphone market and doing a pretty impressive job of it. In 2012, it released its iSport Immersion in-ear model, and I liked it a lot. That model appears to be on the way out, but in the meantime, Monster has also released the iSport Strive and iSport Intensity In-Ear Headphones (the subject of this review), both of which have a more open fit and are not noise-isolation earphones like the Immersions.
Think of these as fancy, hard earbuds that have molded, removable rubber coverings -- Monster calls them OmniTips -- instead of silicone eartips. The design has a couple of advantages. For starters, the earphones are quite comfortable and will appeal to folks who don't like jamming silicone eartips into their ear canals. Like the Bose SIE2i sport headphones, they come with a few different sizes of "wings" to accommodate different ear shapes and help you get a snug fit -- and yes, they do fit securely.
The other positive for some folks will be that the OmniTips let sound in. If you're a runner or biker who for safety reasons wants to be able to hear the external world -- cars in particular -- these allow you do that.
The downside to their open design is that sound quality is significantly impacted by your environment. If you're dealing with a lot of ambient noise, you lose a lot of the lower and higher frequencies and are left with pretty flat sound. (Note: From what Monster PR reps tell me, the slightly cheaper Strive model, which has a different shape to its OmniTips, lets in even more sound than the Intensity.)
Personally, I had good results listening to the Intensity earphones in the gym or at my desk at work. They don't sound incredibly clean or smooth, but the bass does have some kick to it and their sound is a definite notch up from Apple's earbuds, even the new EarPods, which just don't stay in your ears all that well. But outside in the streets of New York they didn't perform as well, with reduced bass response.
The bottom line is that they simply don't offer sound as good as you get from their noise-isolating cousins, the Immersions. Even in a quieter environment, there isn't quite as much bass and they're not as detailed. That said, they still sound decent and measure up to competitors like the Bose SEI2i series and cost $50 less (though the Bose models are arguably slightly more comfortable).