I have had a gekko heat press for many years. It is even heat, but the pressure was off since day one.
It worked when I was only doing sublimation, but doing plastisol transfers and dtg, the press failed to be consistant.
I took the heat pad of and layed a straight edge across and found a large dip in the middle. No amount of increased pressure would flatten out the dip.
I ended up using a product called ALL Metal Body filler, with a painters trim gaurd to squeegee the filler level.
It worked really well!
Now the pressure is even across the base.
WARNING: This stuff says it is resistant to heat, however it will let out a ton of gas and smells once heated and leave residue on the heat pad. Think that stuff is melted polyester gas, so it is BAD to breath.
TO fix that: After the filler hardens completely, wrap the bottom platen in aluminum foil. Do 2 layers, and you should have zero smells or gas leaking out.
Going to use this until I get a hotronix.
edit: Do not do this to the top platen! It will just melt and probably ruin your heat press!
I only did this because it was my only option at the time. Not really a good alternative to a great heatpress