For a small job like that even the siphon blaster will do an adequate job. The pressure may drop because of the compressor cycling but its not like you're getting paid by the hour !!

Keep in mind that no blast media is going to remove the undercoating. Probably the least expensive, most readily available and most effective for your job will be crushed glass.

I just looked at the link ... for the price, I'd spring for that pressure pot. Sell it afterwards if you don't foresee a need for it!