Last week, Purplebricks released its half-year financial results. The top line results include an overall group loss of £27.3 million for the period, with a slight reduction of its full-year revenue guidance. But the top line numbers don't come close to telling the full story (hint: it's not as bad as it sounds).

Why it matters: Purplebricks' core U.K. market continues to grow and is meaningfully profitable, proving that the model works. Key performance indicators in its other three markets reveal a deeper story of investment, growth, and challenges.

Continued growth in the U.K.

The popular narrative is seductive, but factually incorrect: With massive losses at Purplebricks and the demise of online agent Emoov (which, by the way, was not the second largest online agent in the U.K.), the entire online agency business model is near collapse. Not quite.

Purplebricks is an international collection of businesses at various stages of growth. In the U.K., Purplebricks' most mature market, it continues to grow revenues and operating profit. At maturity and scale the business model absolutely works; there is no evidence to support otherwise.

Yes, growth is slowing in the U.K. But at nearly 80,000 instructions per year it can't be expected to keep growing at historic rates. The key is that even in a challenging economic climate, growth continues.

Bumpy ride in Australia

While progress in the U.K. is consistent and positive, Purplebricks' Australian operation has endured a turbulent year. Senior management changes, a business model pivot, and its fair share of negative press has resulted in a "bump in the road" over the last six months.

Revenue growth is up year-on-year, but down from the previous six months, with a corresponding hit in operating profit.

One data point does not make a trend, so all eyes are on the next six months as Purplebricks executes its Australian turnaround plan with a new team and new pricing strategy.

Deep investment in the U.S. market

Purplebricks continues to invest heavily in its U.S. rollout. Over the past six months, it has spent over $20 million on sales and marketing across seven States -- more than double what it spent last year.

Purplebricks managed between 1,200 and 1,400 instructions in the U.S. over the past half-year, or around 200-230 per month. The cost per instruction has dropped from around $21,000 to between $14,000 and $17,000 (each instruction is worth $5,205 in revenue to Purplebricks).

At the current rate, Purplebricks will need to go from 200 to 650 instructions per month to reach breakeven with its sales and marketing costs, and to 1,000 instructions per month to reach profitability.

To achieve profitability, Purplebricks will need to get all of its launch markets performing well, not just L.A. One example is the lackluster performance in Phoenix, as I wrote about last week.

Marketing efficiency

At its core, Purplebricks is as much an advertising company as it is a real estate company. The business model relies on a massive marketing expenditure to generate leads for its network of agents. Thus, one of the most important metrics for the business is marketing efficiency.

For every £1 spent on marketing, Purplebricks generates revenues of £3.60 in the U.K., £0.92 in Australia, £0.36 in the U.S., and £4.38 in Canada (Purplebricks' Canadian acquisition was a fantastic deal).

Strategic implications

The core Purplebricks business model -- and profitability at scale -- is sound. The market failure of smaller players, or the fact that Purplebricks is deeply investing in new markets, doesn't diminish that fact.

From a competitive standpoint, the most dangerous thing about Purplebricks is its investment risk tolerance. It is willing to invest tens-of-millions of dollars year after year to build market share -- incurring big losses along the way. If you're a traditional real estate agency, or a listed company, are you willing to do the same?