Given the tasks it was designed for and the low cost of the unit, the MediaMVP did a good, if not a spectacular, job. The product has been on the market for quite awhile now, and its limited feature set is starting to show its age. The user interface was rather bland, and I would have liked to see native support for more formats both in video and images, but I realize that would have driven up the cost.
More importantly, I also would have liked to see support for the UPnP audio/video standard that's used in most of these types of boxes today. If the box supported UPnP then I could have used it to obtain media from my NAS devices that all run UPnP servers. The fact that it required a Windows system to even boot was a drawback for me as well. I don't want to fire up a noisy, power-hungry computer just to watch a movie or listen to music. The alternative firmwares available would have solved some of my issues had they only supported my version of the box, but I assume this will come in time.
Comparing the MediaMVP to another sub $100 multimedia device - the Buffalo LinkTheater Mini - reveals many similarities. They are both Ethernet-only, networked multimedia players that boot a Linux kernel across the network using tftp and have similar features and form-factors. Both have native support for MPEG1 and 2 video only and rely on a server to transcode other formats.
But there are differences too. The advantages for the MediaMVP include an S-video output, ability to play MP3 files with album art (although without displaying the album art) and large development community producing alternative firmware. The Linktheater Mini's main advantage over the MediaMVP is its support for UPnP AV, which allows it to be used with more devices - as long as you stick to the native formats it supports.
In the end, both of these devices make a lot of compromises to stay under $100. But if the trade-off between cost and features don't bother you, I think you'll find the MediaMVP a nice addition to your home network. And if one of the alternative firmwares works for you, it may just open up a whole new raft of possibilities.