Recent replacement battery health dropping rapidly - safe to use?

I installed an ifixit replacement battery about 3 months ago and it hasn’t worked properly. The battery itself was manufactured a year before it was sold to me, and never behaved like a properly calibrated battery despite following their instructions.

At 34 cycles it had 88% health. Now at 51 cycles it has 73% health.

I haven’t used the laptop much, but always kept it around 50% SoC after calibrating, with some full charges in between.

It seems to be dropping a percentage every day or two. They sent a replacement, but I won’t have a chance to install it for a few weeks. Is it still safe to use in the meantime?