It's an interesting article. If our brains can use quantum computing there has to be some viable mechanism and the article is talking about a paper that claims to have found a candidate. The whole thing depends on quantum effects being important in neurones, which I don't think is something that is widely accepted, the consensus position is probably along the lines of "too wet, too warm, too noisy". So I think the ArXiv article represents a minority position in this field.
The thing about lithium isotopes in rats is interesting, but the article only looks at this unlikely sounding explanation in terms of nuclear spins and quantum coherence without considering alternatives. Since the electron wavefunctions are affected by the mass of the nucleus there is a simpler explanation for the different behaviours of the rats. On the other hand the writer did talk about some of the difficulties, such as free radicals being likely to mess up the quantum coherence the idea needs for it to have any plausibility as a description of nature.