Is dx10 in fsx good or bad and should we use it?

Bad. Should not use it.

DX10 is not complete in FSX. It was meant as preview to full dx10 support that was never finished due to Microsoft closing down the Aces team. Use dx9.

DX10 mode = rick roll

I use it as it makes a massive difference to framerates (on my system). Try it and see.... but be aware it has a few drawbacks.

dx10 makes my fps go over 100fps sometimes over ocean or up in the sky and also over 40-60fps on the ground but it has issues with flickering. I use dx9 and i have a steady fps of 30-40

I would try it. It's just that option in FSX and needs a fresh start, nothing more. Reverting back therefore is easy.

It should be able to give a slight fps increase, while it comes with some downsides on e.g. textures (turning white) or that runway flicker. Those white texture things derive from addons not being dx10-'ready', not from the actual mode. You should see nice cockpit shadows on the models which support it. So you also gain some details.

 

If you want to limit your fps on dx10, maybe use the option in the current Nvidia drivers. The other methods like antilag and that bat file thingy are bound to dx9 only.