The Reanimator can heal themselves for 80hp with a level 1 spell slot.

The new Reanimator has come out and while it seems a bit weak it also seems very tough. The reanimated companion can do many things but at level 15 it becomes a level 1 healing spell that heals 80 hp. The ability life transfer allows a reanimator to sacrifice their companion to transfer its hit points to the artificer. Then with a single level 1 spell slot resummon another companion and do it again. Plus if the companion is damaged the Reanimator can heal it with a lightning damage cantrip like lightning lure. Plus the death explosion damages nearby enemies. That is impressive in my opinion. 

I might be reading the wrong version of reanimator, but i believe life transfer kills the golem, and gives hp equal to your level, rather than gaining the hp of the companion.

Life Transfer. You can siphon the animating magic of your Reanimated Companion to bolster yourself. When you or your companion takes damage, you can take a Reaction to gain a number of Hit Points equal to your companion’s current Hit Points. The companion then immediately drops to 0 Hit Points and dies (triggering its Death Burst trait).

You regain as many hit points as your companion currently has, then you can re-summon them with a level 1 spell slot. That is indeed efficient healing if you only need to heal yourself.

Quote from final101 >>

I might be reading the wrong version of reanimator, but i believe life transfer kills the golem, and gives hp equal to your level, rather than gaining the hp of the companion.

You are looking at the pre-release playtest version of Reanimator from the May 2025 "Horror Subclasses" Unearthed Arcana, which did indeed work that way. The actual published version from Ravenloft: The Horrors Within has a few changes, including Life Transfer now giving you the companion's HP in healing rather than your level.