Just what types of extensions there are and what's best for new riders. I mainly do off trail but every now and then I'll go off trail
There are several types of extensions available. One type is molded into the handgrip, these tend to be on the shorter side. Another type tend to extend out and turn toward the centerline. The finish can be bare metal with a knurled finish or a rubber grip installed. The advantage of the inward turn is it prevents the end from becoming a bayonet in the event of a crash or fall. One of the purposes of handlebar extensions is to allow multiple points to hold the bars to eliminate fatigue. Another purpose on earlier mountain bike was to increase stability when climbing. In my opinion on most modern bikes this is no longer necessary as the changes in gearing and geometry have eliminated the need. There are several downsides. If you have your hands on the extensions they aren't near the brakes. A pretty important criteria for a novice rider. The other minus is the extensions move the shifters and brakes inboard. This can have the affect of a slight change in handling, similar to riding with narrower bars.
In the early - mid 1990's I climbed with a senior emergency room doctor. After a discussion with him on evening, I went home and removed my handle bar extensions and never used them. He dealt with death and trauma every day, when he told me "Those things cause really nasty injuries" and recited recent example of the injures he has treated, I went pale and felt sick, - I had recently had a fall and the extensions had got me exactly where he was describing.
But I don't expect you to just take some random strangers word as fact..... Perhaps a more reputable source - The British Medical Bulletin .
"Large series of patients with liver haematomata sustained during mountain-biking crashes have been reported.34 All of these patients had blunt focal blows to the right side of the abdomen due to the handlebars, and all were using ‘bar ends’ on their handle bars. These forward facing bar extensions allow additional riding positions for comfort and energy efficiency. Following a media information programme of the implication of bar ends for abdominal injury in Austria, bar ends cease to be used in mountain biking. Nehoda's group have noticed an almost complete cessation of liver injury from the sport."
However, these refer to the bar ends common in the 1990's. You can now get grips with a small rubber bar end built in. These are (IMHO) probably much safer.