From over at BJJEE:
They also included a list of some key differences between Judo and BJJ:
"– Judo’s primary way of winning is to throw the opponent flat on their back – winning by ippon. The same technique in BJJ is a score of 2 points and doesn’t end the match.
– Gripping rules / leg attacks – judo has many strict rules against defensive and stalling grips and leg attacks are forbidden. In BJJ nearly any grip – except for fingers inside the sleeves are permitted.
– Match restarts – in Judo if a competitor is not successful with a total commitment throw, they frequently stall in the turtle position and the referee will restart the match in standing position unless their opponent mounts an effective attack that results in progress on the ground.
– Allowed ground time – in an attempt to keep the action as high as possible, judo referees give little time on the ground before restarting the match. Judo newaza has less time for strategy on the ground than BJJ competition.
– Osaekomi scores. In Judo you accrue points the longer you pin someone on the ground. In fact, if you hold someone in a recognised pin for 20 seconds, then you score an Ippon and win the match outright. In BJJ, holding an opponent in side control is not a method to earn points – unless preceded by a guard pass."
Some quick thoughts I would add to that list along with the lack of gripping restrictions is that the overly defensive posture of BJJ Players and the fact that they can sit to guard/pull guard at any time and negate all that work you've been doing is a key consideration.
You'll spend considerably more time in Jiu-Jitsu fighting stiff arms and the death grip of doom than you ever will in Judo. It's not insurmountable, but it does take time to learn to work with/around/against.