Teaparker has tested several tea spoons in this article to see which size and shape yields the best result to smell a tea. Such kind of testing is common procedure for who wants to understand tea, as I've shown recently with gaiwans.
The result of Teaparker's test is that bigger is not better. The small round spoon released more fragrant smells. But size is not everything. The natural glazing on the spoon is important as well. Different glazings will retain the smells for shorter or longer periods.
I actually bought a similiar smaller spoon previously, but found out that it didn't 'perform' as well as my classical chinese soup spoon. Probably because of its cheap coating.
I forgot to mention how you use the spoon: you plunge it into the hot tea and then hold the bottom of the spoon close to your nose to smell the tea fragrances left on the spoon. These tea spoons are especially useful for tea professionals who can't swallow tens, hundreds of teas during tasting sessions. So they use such tea spoons to just smell the tea.
So, the best advice I can give is: make your own test to find which is your best tea spoon. This exercise will have the added advantage to train your sense of smell and your concentration.