you might be right that you are not stuck with THAT agent but with AN agent. Your visa history will become so "polluted" that it will need money to make it happen. If you just go by yourself next year, then your visa will most likely be denied and you risk a long ban from entering Thailand based on staying in Thailand in the past on no legal basis... You'll make your own destiny...
, ok, så what you mean is METV plus a few extended visa exemptions. This will mean quite a few border bounces as the METV takes a few also. You obviously take the risk of being denied entry at some point.
, you need to be a little careful with the ED visa that you do actually study. There are still many offers around for faked ED visas, but you might end up getting banned from entering Thailand or getting another long stay visa later on...