SYS is basically OVH’s lower-end offering that still provides SLAs and better bandwidth (they have an even cheaper offering called Kimsufi but no SLA on those - though great value for staging/non-critical systems).
The experience is mostly solid, though they don’t provide any kind of console access and I once got locked out after putting a machine to sleep from the command line (and had to open a ticket for someone to reboot it manually).
The "problem" is that this is not a virtual machine and most assumptions or ways of thinking that work for AWS or similar don't work here. For example, you can't just upload an image or move data volumes around between machines. The storage volume is a physical disk attached to the machine, if you need to copy them you need to actually boot the machine, SSH into it and do your thing. Similarly, those disks can break down and you need to plan ahead (they provide 2 disks per machine and expect you to use a software RAID 1 or have a backup/restore strategy that can tolerate those disks failing).
This is where building your own layer on top of it (whether Kubernetes or VMWare or similar) makes sense and will make your life easier and allow you to use most tools we take for granted when it comes to VM providers - you're essentially building your own AWS.
This is a whole other league compared to Linode - the former provides VM instances with varying levels of performance - the one we’re talking about is bare-metal and you are guaranteed to have the performance of whatever hardware specs you chose. Bandwidth is also unmetered so you can saturate the pipe 24/7 if you wanted to. Very cost-effective for serving media, though every machine only comes with 250Mbps, so maybe it's better to have an origin server on SYS, and lots of downstream instances on Kimsufi which serve as a downstream cache for the origin - they are dirt-cheap and come with 100Mbps bandwidth each (unmetered as well).