What are the disadvantages of mana?

Could you elaborate on the drawbacks associated with Mana? Are there any specific limitations or challenges one might encounter while utilizing this cryptocurrency? Additionally, how does the volatility of Mana's price affect its overall usability and acceptability as a means of payment or investment? Furthermore, what are the potential security risks involved in holding or transacting with Mana? Finally, how does it fare compared to other cryptocurrencies in terms of scalability, transaction speed, and cost-efficiency?