Often a question we see online for those interested in purchasing a flat bed is for machine recommendations however the first question really should be what fiber will I most often be wanting to work with so Incan choose a gauge machine that works best.
I started my machine knitting journey with a circular sock knitting machine which works best with light to fingering weight sock yarn - therefore this is the fiber I have the most of.
Therefore for me and what I will want to make - the standard gauge machines work best.
See this fantastic site for a guide on what yarn weights to use
I was extremely fortunate in being given a stash of supplies along with a flat bed - even though after machine servicing it was deemed a write off - all the bits were still very usable so I found another machine online and was lucky to have it arrive in one piece undamaged. See the stash.
So once you’ve decided what gauge machine you need to consider whether you wish a plain Jane model that is completely manual or one with accessories like a punch card and then again whether you want an electric model.
Then once you’ve given yourself a short list consider if your game for the risk of a used machine (not what it’s said to be, poorly shipped etc) or a new machine.
Used isn’t bad and either way you go you will need to consider becoming familiar with care and machine part names etc.
My Singer SK700 has long since been discontinued however it was made in 1986 and isn’t electronic so other than maintenance-the real issue is plastic durability through time.
In my opinion why get a super simple basic manually run machine when you can get one with a few options you can learn to use later?