As a beer brewer, I'm pretty concerned with fizz ;) Since the below may be a little tl;dr, the short answer to your question is, "I don't think so."
This is actually the first time I've heard of the metal spoon "trick", so I can't directly comment on that, but I'll share a little of what I know about carbonation.
Carbonation is carbon dioxide (CO2) that is dissolved in the liquid (beer, champagne, soda). The fizz is that CO2 coming out of solution and escaping into the air.
Keeping it cold helps keep the fizz, as CO2 dissolves more readily into a cold liquid. And conversely, comes out of a warm liquid more readily. Ever pour a glass of warm soda or champagne straight after opening? It'll foam over everywhere.
The only way to not lose all that CO2 is to seal the container. Even then, the CO2 will come out of solution and pressurize the headspace (space in the top of the container). That's why you get a hiss when you first open a bottle.
Again, temperature comes into play. In a warm bottle, more of the CO2 comes out of solution and pressurizes the headspace. Chill that same bottle down, and the CO2 can dissolve back into the liquid, giving you a sparkling beverage again.
Now, back to the spoon. I would think that putting a spoon in the carbonation liquid would produce nucleation points, causing the CO2 to come out of solution faster. This is why many beer glass manufacturers are coming out with laser-etched designs on the bottom of their glasses - the effervescence caused by the nucleation points helps bring out the hop aromas.
As identified in my original comment, the most likely risk is not from the container itself, but from the fact that it's meant to be used with an immersion blender.
Heat actually isn't a major problem with polypropylene (PP). It's generally regarded as food-safe and is BPA-free (see here and here for references), and its melting point is somewhere between 130°C (266°F) and 171°C (340°F) depending on its specific crystalline configuration (or isotacticity). So you could even pour boiling water into a PP container without major risk of deformation - just don't try to bake a casserole in it or anything.
PP is often injection-molded, which can leave molding seams; these could be weak points in a closed vessel containing a carbonated beverage. But that's not really a concern with an open container.
Once you introduce an immersion blender with fast-moving blades, though, you've got the potential for hot liquids to be flung outwards if not fully submerged, causing possible risk for burns. Those blades will also intensely agitate carbonated beverages, causing a release of CO2 and extensive fizzing. The biggest reason not to use an immersion blender with these is probably that you'll lose half of the volume to spillage, and agitate the rest to the point of losing its carbonation.
Best Answer
Carbonation produces the textural effects associated with effervescence, first of all, and a lot of people find that texture enjoyable. Texture is a huge part of the culinary experience and affects how flavorful compounds contact your tongue, thus affecting its perceived flavor.
Carbonation also raises the acidity of a beverage slightly, due to the presence of dissolved carbonic acid in the solution. As @Joe mentions in comments, this can promote the release of gasses with additional dissolved flavorful compounds. All of this can have a suppressing or enhancing effect on other flavors (a topic which is absurdly complicated and still being explored by food scientists much smarter than I).
Basically, the point of carbonating is similar to the point of pureeing something, or the point of dehydrating it. It's a fun and easy way to change how you experience the food--or beverage in this case.