No, they are not "bad". They are not any worse than a standard SSD except they are a bit more expensive in some cases but that seems to be rapidly changing, with prices lower than they've ever been on storage currently.
I would avoid the Kingston drives though. They are questionable.
I would recommend sticking to, in order of preference, Samsung, Crucial, SanDisk, Intel, Corsair and Western digital.
The question isn't about M.2, because there are SATA M.2 drives that are no faster than a standard SSD. The question is about whether or not you could benefit from a PCIe NVME M.2 drive, and for most people the answer to that is yes, but it depends on what you do as to whether or not it's really beneficial to you or not. In truth, if it fits your budget there is very little reason to NOT choose an NVME M.2 drive these days. It's smaller, uses less room, no cables running around, faster in both random and sequential operations and even in cases where there is a long sequential operation and the drive throttles itself, it is still going to usually be miles faster than a SATA drive IF you are transferring to or from media that is just as fast.
The best setup would be M.2 SSD for the operating system to live on and then a secondary standard SSD (Or a second M.2 NVME SSD if you can afford to get one in a size large enough for your needs, which many people cannot). If you can get by with a 250 or 500GB primary drive for the OS and a 1TB secondary NVME drive for other stuff, that would make for a very fast system in all access operations and especially in transferring anything between those drives.