I've been using them for a few days now. My normal set up is a 510 with a 901 filler cart (straw mod) on a 3.7v AA box mod, 100% PG juice.
They draw about the same as a filler cart. Haven't had any leaks (though there's a lot of condensation in the tank cart). Good vapor production, taste is better than with the filler cart. Haven't had any dry hits.
My one complaint is that the carts are small, and I empty one in about 45 mins to an hour of moderate
vaping. There's a non-Joye XL cart being made for it that I'm going to try soon.
As to the syringe . . . not necessary. The bottom of the tank cart can be pried off fairly simply. A syringe MAY be more convenient, however, but it's not required.