TL;DR, short answer: NO, THEY ARE TOTALLY NOT SAFE TO DIVE WITH! YOU WILL DIE.
If you check out the description of such gimmicky gadgets, you will notice that they're billed as "pony bottles / last resort air source", to be used by trained, fully equipped divers as a backup only (side note: those "pony bottles" are generally frowned upon and their use is discouraged by instructors / experienced divers, as they actually add more risks and danger... but that's out of the scope of this question).
Why those bottles cannot be used as a standalone diving air source? Because they miss one critical component - a buoyancy compensation device (a wing/jacket worn by divers). Without it a diver would not be able to control depth and either fall down quickly, run out of gas and die, or would descend normally, then ascend too quickly, suffer lung barotrauma from the expanding gas and die. Contrary to the common belief, dives to shallow depths up to 10m/33' are the most dangerous from the barotrauma point of view — during an ascent from 10m to the surface the gas inside your lungs/inner ear would expand its volume TWICE. Guess what happens next! Yes, you'll die :)
Then, there is a specific concern related to those pony bottles. They're very small in volume, meaning low amount of breathable gas.
Here's a quick calculation: my SAC (breathing rate on the surface) is around 20L/min. Those Smaco 1 litre bottle can be pumped up to 200 bars, which would give us 200 litres of air. That's theoretically good enough for ten minutes of breathing (that's on the surface! if you'd dive to 10m, you'd halve the time due to higher ambient pressure).
However, you'd not just sit underwater, you'd swim and would want to look around, which, with added excitement, significantly increases gas consumption. When I measured my consumption during strenuous swimming, it went over 80L/min, meaning a little over one minute of breathing at 10 metres.
Now, to address your specific situation (an ex-navy diver dad): wearing a jacket with a proper bottle is not actually very strenuous, I've seen people in advanced age go diving... and there're smaller bottles if you're concerned about bulk/weight (I think 5L or so is the smallest tank used for breathing gas).
Then, there's another style of diving called "sidemount", where you wear only a lightweight wing/harness, go into the water then clip the tanks with gas to yourself (you basically don't feel the weight of the tanks when underwater). When you go out, you unclip the tanks and some strong young lad takes them from you :)
This is what I would actually recommend, if your dad really wants to go back into diving but is concerned about weight/his knees/back. Note that YOU CANNOT teach yourself how to dive from Internet forums, one needs to learn from a certified instructor (otherwise, you will die).
Coming back to the pony bottles. The only way they could be used safely for diving is when "diving" in a backyard pool of less than 2m/6' depth, where you could simply stand up in case of any problems / running out of gas. If the pool is deeper - you will die!