Hello, I have been testing depletion with the material transfer rates feature and found it extremely slow (multiple days runtime). At first I thought that the problem was in the solver (since the matrix becomes huge and the depletion problem is solved in a single-threaded fashion) but then I discovered that the problem is actually in the form_rr_term method of deplete.chain.
There are some optimisation candidates in the v0.15.3 implementation, mainly the fact that components = tr_rates.get_components(mat, current_timestep) gets called inside the nuclide loop. After having the method optimised, the runtime drops from days to minutes (for my problem).