There is a place here near me that sells this sauce. I look for stuff low carb (1g) low sugar (1g) It is very good on roast beef. Sure it good on other stuff.
I know their horseradish cheddar isn't low carb, but I highly recommend it when you are able to treat yourself to something different. It's fantastic with pastrami.
I just ordered some Zanerains Horseradish sause, and I use it as a base: it's great. Hard to find, so I ordered it online. Got a bag of horseradish powder too (I'm goin that way as a cook: using powders as my bases so as to control flavors). Highly recommend both.