No personal experience with Thompson's.
Thompson's makes a sealant specifically for cloth and leather; is that what you're referring to? The website says it allows the fabric to breath, so I'd think it's got to just be a DWR coating like Mcnett, Revivex, etc. I've generally had good results with Nikwax products.
How was your tent leaking? Bleeding through the fabric, seams, etc.? If it's silnylon or PU coated nylon and its wetting out the fabric to the point of leakage, a fresh coat of DWR might be a very short term (or not at all) fix.
