The worm screw on mincer should ideally be turning about 80rpm (let's say 50 to bit over 100). Basically no cheap mincer (including the linked Tre Spade) does that. And it's useless to compare claimed motor output, there are so many other things that affect the produce and longevity. Remember the cheap ones are very noisy, to the point you want to use ear muffs while mincing (Tre Spade should be quiet enough).
You're neither going to get (stainless) steel parts, below maybe £500-700 or so. In Chinese crap, stuff that looks like stainless is polished aluminium. And in European machines the worm screw and it's housing are cast iron, plated with tin or some similar stuff. Problem with that is, over time the plating starts to chip off and only thing you can do is replace parts (or accept that your produce might have a piece of plating here or there). Also you must hand wash them, preferably dry soon and coat with parafin oil or similar.
Largest problem is that people tend not to trim the minced meat properly. And because cheap machines lack power/torque, have oversized hole plates (4.5mm is about the largest that can properly cope with poorly trimmed meat, but it needs torque) and poor worm screw to housing fit -> the produce is poor. Sadly the screw to housing fit can only be judged when you have the machine in hand, even though it's one of the most critical qualities.
Like said the cutter can be easily honed with diamond or flat plate and fine emery paper. Try to get curved blade, if possible. Also try to keep the hole plate aligned the same, it helps with the blade. Eventually the hole plate also needs honing. Other wearable parts include the stud in front of worm screw, that goes into the hole plate. In standardized designs, like the Tre Spade linked, you can get replacement parts easily and reasonable cost. In household items you'r probably screwed...