What you've bought will work and probably last for a few years with light use and good care. What you're getting with the more expensive higher powered options in the ease of use and speed. The cordless knives can be used anywhere and drop cords/outlets being available are removed from the fish cleaning equation. The more expensive higher powered knives also make the job easier thus saving you time and making you less tired at the end of the day. The old adage of "you get what you pay for" is very applicable to most tools and this is a tool to perform the fish cleaning task.
I understand your thought process and I did the same thing when I first turned to electric knives. I weighed price more heavily than other factors and purchased several cheap knives only to find they didn't work great and didn't last long. I've had the Hamilton beach, Black and Decker, Rapala, etc. The Rapala was by far the worst I had. Hopefully the HD model is better for those who choose it.
My experience may be different than yours as we clean hundreds of stripers and quite a large number of catfish each year along with the crappie/panfish. That makes my experience a little tougher on knives than the hard core crappie only angler.
At the end of the day use your own judgement and learn from your own fails/wins. Hopefully my fails can help the rest of you. :banghead
Chris