This illustration shows many of the challenges using propulsive deorbiting:
https://www.smithsonianmag.com/air-space-magazine/34_aug2017-cleaning-up-space-junk-180963932
The trust line of the tug is aimed nowhere near the center of mass of the debris. The majority of thrust will produce angular momentum, not retrograde thrust.
The trust direction has a radial component , which is a waste for deorbiting. Useful thrust is retrograde. Out-of-plane thrust is a complete waste. Radial thrust is inefficient.
If this is a single-use tug, it will re-enter with the debris, an inefficient use of its launch costs.
If this is a multi-use tug, it will need to prograde burn to climb back up to service altitude.
Single-point grapple makes for unreliable thrust alignment during burn.
If propulsive junk deorbiting is to be worthwhile, it must make economical use of resources. Propulsion must be retrograde and through the center of mass. Multi-use “motherships” for rendezvous must not be put on a re-entry orbit by the retrograde burn.
Are there any propulsive deorbit proposals which answer these challenges?