If they spend $0.99 for $1 of MRR, that is amazing, because the first month's revenue covers the cost of acquisition and the rest of the stream is profit (minus other expenses of course.)
Some of it depends on churn and how much MRR you lose and how quickly.
We'd look at an objective function of LTV to CAC ratio.
We'd ignore everything below a certain absolute MRR.
We'd also ignore anything below a certain MRR growth rate.
The ones we'd typically look at as an investor are: MRR/ARR, Churn, CAC and TLV.
TLV would be total lifetime value which includes the monthly revenue * months given churn.
CAC would be the advertisement cost.
This basically means, how much $ are you spending to make what total $ per customer, and how what is the volume.
MRR is meaningless in larger startups because for all intents and purposes would be eaten by the salaries in two seconds, unless it's huge. At any point it becomes reported as annual revenue.
Successful startups spend more like $1.25 per $1 of MRR.
Profit is for solo founders and bootstrapers.