Why does Putin favour an apparently inefficient poison

I've been trying understand why Putin and his lackeys persist in using a very inefficient Soviet-era poison.
Poison has long been a favourite Russian tactic, dating back to the 17th century and even earlier, and the Kremlin in particular has employed it to great effect since the 1920s. The Novichok nerve agent, which was used recently against opposition politician Alexei Navalny, and against defected military intelligence officer Sergei Skripal and his daughter in 2018, was developed by the Soviets back in the 1970s. In both of these recent cases, the poisonings were not fatal, and moreover were easily identifiable as of Russian state origin. So why would Putin use such an obvious and apparently inefficient means to attack his enemies. Wouldn't a good old fashioned gun do the job better? Or even a more effective, or less identifiable, poison?
Well, it seems that identifiable is just what Putin is aiming for. Novichok is often fatal (the most recent victims were lucky to have good, fast medical attention), and anyone who is treated to it is left in no doubt (and in a very public way) that Vladimir Putin wants them dead, and could easily bring that about at any time or in any place. It is more a threat than an earnest assassination attempt. It sends a very clear message, delays investigations, and sows confusion.
Poisons often work excruciatingly slowly and painfully, adding whole theatrical aspect to the deed. And, while pretty much everyone knows that Putin is behind the attacks, there is no smoking gun (so to speak) that can openly be attributed to him. There is a "veneer of plausible deniability", and it is relatively easy to blame existing health conditions or environment factors or on other agents seeking to discredit the government.
Putin is supremely confident of his position and his international strength, and is not unduly worried about a bit more bad press. Neither is he worried about whether his actions are perceived as honourable or not Plus, we are not talking about a death, merely a major inconvenience (and possibly lasting medical issues), which arguably dials down the stakes a little.
As one unidentified European functionary commented,"Putin is confident he can take more pain than they can. Until that changes, I fear he can kill all the Russians he wants."