Everyone will probably agree that this is not a mistake.
Generally briquettes are cheaper for the most part, and a nice steady burn is easy to maintain.
I use an SNS as well for a few low n slow cooks......and have used both charcoals....lump mostly.
My main concerns are....
Make sure you get it all in there good so it stays lit......the quality of the lump may play a part, not sure, it's been a while since I used the cheaper crap around here. If you have the deluxe SNS watch the water, it will need to be topped up about every 3 to 4 hours....mine now has a pretty good warp in it from just not paying attention. You should get 5 - 6 hours easy on low before you need to top up the fuel.
You may find it harder to maintain a real low n slow.....temps like 230 are going to be harder to achieve without playing with it constantly...
Mine likes to hold at 250 - 265 if I want to just sort of forget about it and let it do it's thing......smoking wood increases the temps more than I want it to.
Most of my smoking is done with the E6 because it does a great job and gives me more area to work with.