I would say it depends on the size of the system you are backing up, how long you want to store backups for, and whether the backup solution is going to be permanent or temporary.
Using Manything as an example, to backup/cloud record with them you need their cloud adaptor (which is £99) plus the monthly subscription plan. (which starts at £3.99 to store footage from 1 camera for 2 days)
So to backup 2 days worth of recording continually from one camera for 2 years would cost you £194.76 (including the cloud adaptor)
If it was just a 1-4 camera system you could get another 4-channel Hikvision NVR [DS-7604NI-K1/4P(B)] without a HDD for less than £200
Basically, if you have a system of 4 cameras or less and you only need 1-2 days of continuous recording then cloud recording can be an option, but for systems greater than 4 cameras the subscription cost rises to a point where it is more cost-effective to purchase a 2nd NVR. (Manything's 5 camera/2 day recording plan is £12.99 a month, which is £410.76 with the cloud adaptor)