First of all , lets make it clear and I wish that all of you will understand it.
There is no such animal called "unlimited or unmetered" . There is always limits and if you exceed the regular fair use or normal use you will be asked to move to higher plan or VPS. Unlimited = Marketing trick
The difference of managed and unmanaged was explained fairly well from the previous posters. However depending on the hosting provider you still get support even on unmanaged servers.
For reference we are offering semi-managed and fully managed offshore vps servers . With semi-managed we deliver fully configured and secured VPS with pre-installed Control Panel (Paid or Free options).
With semi-managed we are monitoring your server uptime and also protect it from DDOS up to 500Gbps. We however are not keeping upgraded the VPS for you .
With managed VPS however you are still getting only technical support that DON'T cover isseus with 3rd party scripts. Also with managed vps you are receiving free daily / weekly backups of your VPS.
Managed VPS hosting is x2++ of the semi-managed vps prices, it may or may not include cPanel license. Now if hosting provider provide you with cPanel that doesn't automaticaly means that is fully managed. You better contact the hosting provider prior purchasing. Also would be nice if you can find out if the provider is not reseller .
Best Regards,
CyberHour