If you are developing you should have no issues learning how to install apps through ADB commands. This allows you to side load apps via a USB cable. If you are carrying an Incredible you probably will be disappointed with the Backflip. However if you are looking for lower end devices to test your apps the Backflip would be a good choice.

 

As kirbo20 mentioned, you will have no issues installing your apps through the SDK. As far as testing during development, it will work exactly the same way as the Incredible; all you have to do is have it plugged in via USB, install the drivers, and then it will show up in your deploy list from Eclipse exactly like your Incredible. Just press Run and it will deploy it and install. For other APK files that you get from other sources you would just plug in the phone, type `adb install <apk-filename>` and it will install the APK file straight on your phone. All that option affects is the ability to download and install an APK file straight on the phone without going through the computer.

Oh, and as far as testing on an HTC device with a custom ROM, that might not be the best route to take, since the ROMS have a tendency to be a bit buggy at times, and things that wouldn't crash a regular phone with android preinstalled might crash that phone, or vice-versa. I had android installed on my Tilt for a while, and it was definitely an entirely different experience than I have with my backflip. Now if you have one laying around you might give it a shot to have one more device to test on, especially since it is easy to have various different OS versions to test with, but as far as using it as one of your main development phones, that probably wouldn't be the best idea.

 

I have both an Incredible and a Backflip, and I am not dissappointed by either one. If you do your homework, you understand the limitations of each, and expect them to work according to how they are programmed. I don't think that you will be dissappointed at all with the Backflip, especially for that limited amount of time since you are knowledgeble of its capabilities.

 

For what it is, the BACKFLIP is a very cool device.

I have a DROID that I use for work, after hearing me talk about Android day after day my wife wanted one and since our personal phones are on AT&T I got her the BACKFLIP. She had never used a smartphone before and it took her some time to get used to it but now that she's been using it for a while she's pretty much mastered it.

It's slower and smaller than the DROID - I don't think I could ever use one myself - but for a casual user who wants the power of Android and wants a physical QWERTY keyboard it's a nice little device. The voice quality is very good and it gets better reception than my RAZR does when we're both in the same spot.

As for developing and testing, I've got no experience with that but the other replies in this thread should help you out.