why wouldn't it be? clots used to do it a few years back and were very successful using that tactic... that was pre-2018 though, when the rule changes kicked in...
since then, on-side kick conversion success has been miserable, with the conversion rate dropping dramatically... a surprise onside kick was successful about 60%, an expected onsides kick 20% of the time iirc... after the 2018 rule changes, a conversion was successful 8% of the time, and in 2019 just 6% of the time... not sure about 2020... couldn't find those numbers..