If you loose power while flashing, you just need to be careful to not turn the car off and as long as you don't, you can then restart the process. The way EcuFlash/OpenPort works is to send a kernel in to your ECU. That bit of software oversees the reflashing process. If the process is interrupted (laptop goes to sleep, USB unplugs, etc) you can correct the problem and restart the process with no ill effects because the kernel is waiting patiently for new instructions and it will even pick up where it left off. However, if you turn off the car after a mid-flash problem, the kernel is now gone and your ECU is bricked.
As for the benefit of the OpenPort over a VAG-COM cable, for one you have fast logging functionality built in to the hardware which allows you to easily log on the go without a laptop connected. You also have the latest driver that we've written for increased stability over the older versions which used Windows software, which wasn't as stable. We wrote our own driver when we were seeing occasional Window's blue screens. Is the savings of a Chinese VAG-COM worth the increased risk of OS crashing? Is increased stability of value to you? If you know anything about Windows driver development, you know that it's very challenging work.
Why do we do we spend timing working on better drivers, new software features, new vehicle support, and OS issues? We spend time on OS issues (upcoming release has improved install for Windows Vista), new features, and new vehicle support (two addition ECUs in the works now), because supporting and creating a better product for the community is the focus of our company. Our daily work is funded by the sales of the OpenPort. We're currently hiring a support person (in SF if you know someone) and eventually we'd like to add a third full time developer.
You should consider purchasing an OpenPort because it's assembled in both Washington and California, not overseas, so sales supports physical labor in two US states and two companies. Your purchase supports EcuFlash development. You receive lifetime support with our hardware & software, even if you aren't the original owner. Pretty good no? You support the growing of a small business that works to make tools of value to this community. We think those facts make us pretty unique in this space and good reasons to consider purchasing our hardware to support US production and development of an affordable product.