Given that the 'efficiency' of Peltier/Seebeck/thermoelectric systems is very, very bad — even under ideal conditions — if one manufacturer comes up with a low-efficiency design, you are effectively comparing very, very bad with very, very, very bad.
If you want one of these things because they just look cool, then fine. If you want to use it to impress your friends, then fine. If you want to use it as an educational tool, then fine. If you are off-grid and have zero access to electricity, then fine. Otherwise, if you just want to mix the air in your room efficiently and inexpensively, consider the following:
A 'large' 12V computer fan (e.g. the 200mm NF-A20 FLX from Noctua) can draw less than 1W when running at maximum speed (actually 0.96W @ 800RPM). All 3-pin fans can run at lower speeds (and be much quieter) by simply dropping the voltage. A Low Noise Adapter is included with each of the above fans, does just that, and drops RPM down to 550 and power draw to 0.66W. At that speed it's virtually silent and circulates 100.8m³ per hour — which I suspect would be more than sufficient to meet your needs.
If your search showed thermoelectric stove fans ranging between £25 and £100, then the middle of that range would be £62.50. Given that a NF-A20 costs £27 from Amazon.uk with free delivery, you'd have £35.50 left over if you bought one of those instead. If you are paying 15p/kWh, then £35.50 would pay for 236.667kWh of electricity. It would take the NF-A20 about (236667/0.66=) 355,000 hours / 14,791 days / 40.5 years of continuous use to consume 236.667kWh of electricity.
The Mean Time Between Failure of the NF-A20 is 150,000 hours / 6,250 days / 17.1 years of continuous use and Noctua backs that up with a 6-year warranty. By contrast, most thermoelectric stove fans have warranties of only a year and die around then. Some of the better ones have 2 year warranties. I haven't personally seen any with a 3 year (or longer) warranty. I doubt that any have a 6 year warranty. Most of the ones I've read about lasted between 1 and 2 years before failing.
- thermoelectric stove fans on a seasonal duty cycle last ~2 years
- computer fans on continuous cycle can last ~17 years
- the money you save buying the latter can power it for ~40 years
A little bit of easy math shows that thermoelectric stove fans don't make financial sense if you have access to electricity and mixing air efficiently and inexpensively is what you are actually trying to accomplish.
Computer fans are not the only way to mix air, of course. Even a regular ceiling fan would probably end up cheaper (and be more effective) in the long run. You can also do the same thing with some copper/aluminium pipe and a pipe bender — although that is definitely a different aesthetic. There are lots of choices (none of which exploit the thermoelectric effect, and some of which are completely passive).
Before spending money on a thermoelectric stove fan of any kind, I'd encourage you to look into the other options.
In essence, thermoelectric stove fans are primarily an expensive gimmick/toy. It makes virtually no sense for the vast majority of the population to buy one.