Platform as a service (PaaS) company Twilio Inc’s (NYSE:TWLO) stock price has continued to struggle so far this year. It follows a tough fall 2016, when the stock briefly catapulted past $70 per share (September 2016). Since then, TWLO has fallen some 65% to a current $25.25.

Twilio stock swoon may make it look like the shares are trading at an appealing level right now, but TWLO is still very difficult to value.

Sales have literally skyrocketed since the company was founded in 2008, but Twilio has yet to achieve annual profit, or cash flows. That being said, the firm is a true leader as a major platform in cloud communications.

Customer concentration is a key concern among investors. Uber, the ubiquitous and fast-growing ride sharing company, is a top customer and accounts for more than 10% of total sales. During Twilio’s first quarter, Uber made up 12% of the total top line.

The problem is that Uber is diversifying to other providers, as well as its own internal communication services. In TWLO management’s words (from the latest conference call transcript), Uber is moving to a “more active multi sourcing program.”

TWLO Is Among Behemoth Competitors

WhatsApp is another big customer, also at roughly 10% of sales. After that, Twilio said its third largest client is only about 2% of the top line. So, the top 10 customers make up approximately 30% of sales. It’s certainly a concern, but the overall client base represents a who’s who of cloud-based software and tech firms.

Other customers include OpenTable Inc, Lyft (Uber’s archrival), Intuit Inc. (NASDAQ:INTU), salesforce.com, inc. (NYSE:CRM), DocuSign, and Box Inc (NYSE:BOX). Most are growing sales rapidly, so as a result Twilio should be able to keep its sales pipeline healthy. Amazon.com, Inc. (NASDAQ:AMZN) Web Services (AWS) is also a customer, and the relationship appears to be growing.

There is little denying Twilio’s relevance in cloud-based computing and letting companies talk with their customers. To use Uber as an example, Twilio lets drivers talk with passengers through Uber’s app, as well as via phone, text and voice. It’s the essence of how companies want to communicate with clients digitally.

Unfortunately, it’s also an extremely competitive subset of the tech industry. As Uber indicates, customer loyalty is an issue. And, SAP SE (ADR) (NYSE:SAP) and Oracle Corporation (NYSE:ORCL) are the 800-pound gorillas in enterprise software with whom TWLO must compete. Salesforce and Workday Inc (NYSE:WDAY) are other, more direct competitors to Twilio, though they operate more specifically in corporate sales and finance/human resource departments, respectively. Yet, they are also formidable and deep-pocketed rivals.

The rub with investing in many of the cloud-based upstart companies is the profit visibility. Twilio has yet to post an annual profit since incorporating. This year, analysts collectively project an earnings loss of 29 cents per share. In 2018, it gets only slightly better — the consensus estimate is a loss of 9 cents per share. This suggests profitability could still be two years, or more, down the road.

Twilio’s free cash flow is also still negative. Since its founding, TWLO has lost (or “spent”) $201 million, which is the accumulated deficit on its balance sheet. Of the $539 million it has raised from investors, only $338 million is left, most of which, luckily, remains as cash in the bank.

Bottom Line for Twilio Stock

So, what is Twilio worth? My colleague, Will Ashworth, framed it well in a recent article, questioning whether TWLO stock will go to $15 or $30. It is a good question, but until profits start coming in, it could be either.

My primary valuation measure (analyzing free cash flow and discounting it back for a present value share price) isn’t of much use when a company is reporting losses. Of course, any value is predicated on cash flows eventually becoming positive.

Until Twilio starts generating more consistent free cash flow, I’ll do more work on trying to discern if its business model is truly unique amid the cloud-based competition. TWLO says it is “three things” — a programmable communications cloud, super network (or namely a “globally interconnected software powering flywheel of growth”) and a business model for innovators.

It all sounds great, but currently only a select handful of new-era tech stocks have demonstrated a proven ability to both grow sales and generate impressive cash flows. Alphabet Inc (NASDAQ:GOOGL, NASDAQ:GOOG) and Facebook Inc (NASDAQ:FB) are two current winners, and their valuations of around 30 times earnings look visible and stable compared to upstarts such as TWLO. It’s a key reason their shares are experiencing price appreciation, which is also accounting for a large share of total stock market returns.

As of this writing, Ryan Fuhrmann owned shares of Alphabet and Facebook.