I personally have never experienced a benefit to running deca at a dosage lower than 300mgs/week. Might there be some therapeutic benefits? Possibly. But it isnt going to add a noticable difference as far as mass IMO. If this is something your HRT clinic is promoting, its just an add on they sell to increase revenue (again only my opinion).
I don't know your age or anything, but some of the more openminded HRT clinics are starting to sell HGH or GHRP's. If your north of 40 or 45 this might be worth the money. But it will be expensive. Nothing else my doctor has offered has been offered in anything close to sufficient dosing to add any real benefit for my personal goal.
Once you get your HRT dose dialed in you will likely only have to go for blood tests every 6 months. That's what I do, leaving me six month windows of opportunity to supplement my HRT with whatever I want, at whatever dosing I want, and scale back well before my biannual blood draw visits.
If you want to run deca, buy from one of the sources in the sponser section and run it at a level to provide benefits IMO.