Tricep tendonitis - bands or DBs?

[ReboundReps]

I was prescribed slow tempo tricep exercises (3 secs up and 3 secs down) a while back by my PT for my tricep tendonitis.
So I decided on lying triceps extensions with DBs.

I originally started with around 1kg DBs but now I'm at the point of doing 3 sets of 10 reps with 4KG dumbbells, but thats with 6 seconds per rep.

However I seem to be 'stuck' at this point, if I try going to 5KG or doing more reps then the pain creeps back in.

The above actually feels very challenging where I barely even have the strength to do it, so I imagine it's too much for my tendon too

Should I maybe switch to bands instead of DBs?