Is Apple TV Plus — the tech giant’s foray into the streaming wars — a roaring success?

That’s been the initial takeaway from estimates by research firm Ampere Analysis, which has pegged Apple TV Plus as having racked up 33.6 million customers in the U.S. alone as of the end of 2019. As initially reported by the Wall Street Journal, Ampere’s guesstimate would mean Apple TV Plus is bigger than both Hulu (which the firm estimates had 31.8 million users) and Disney Plus (23.2 million) in Q4.

But a few big caveats are in order.

For starters, the U.K.-based researcher’s numbers are “very early-stage, initial estimates,” Ampere Analysis research manager Daniel Gadher told Variety.

Moreover, Apple TV Plus has very few paying subs: The “vast majority” of those estimated 33.6 million U.S. users who signed up after the Nov. 1 launch are getting the service under a one-year-free offer from Apple, according to Ampere. The company doesn’t have a specific breakdown of how many Apple TV Plus users are actually paying the regular $4.99 monthly price for the service.

Under Apple’s deal, Apple TV Plus is free for 12 months with the purchase of any new iPhone, iPad, Apple TV, Mac or iPod touch device. Customers have up to three months after first setting up their device to claim the offer. For Apple, the fact that few customers will be paying subscribers “should not matter for Apple financials – as Apple TV Plus at this point can be seen as supporting the device business,” Gadher said.

A major question is how many Apple TV Plus users who are currently getting it for free will end up paying for it — which may be tough sell, as its originals lineup is far smaller than many of its rivals. Ampere modeled out replacement rates for devices across different markets, including the U.S., to arrive at an estimate of about 40 million total Apple TV Plus subs by the end 2020 in the U.S.

The challenge for Apple “will be keeping these users engaged on an ongoing basis,” said Ampere’s Gadher. “Given the small size of the Apple TV Plus catalog we would expect a lower usage rate compared with other platforms with larger catalogs.”

Apple TV Plus currently offers 16 original TV series and movies, including “The Morning Show” starring Jennifer Aniston, Reese Witherspoon and Steve Carell; M. Night Shyamalan’s thriller “Servant”; “Oprah’s Book Club”; and Kumail Nanjiani and Emily V. Gordon’s docu-series “Little America.”

By the way, in the U.S., Disney Plus — like Apple TV Plus — is benefiting from a free promotional giveaway. Disney has a pact with Verizon to give away a free year of the Mouse House’s streaming service to customers on unlimited wireless phone plans and new Fios broadband customers. Analysts have estimated that about one-third of Disney Plus’ initial sub base has come via the Verizon partnership.

To calculate its estimates for Apple TV Plus, Ampere gauged the number of Apple devices in the market and unique households that own the company’s products (using its consumer polling data). Gadher noted that there’s a margin of error with Ampere Analysis’ estimates but said it was difficult to provide “a specific statistically valid margin of error.”

“What we can say is that we will be monitoring uptake, and particularly usage, closely,” he said, using Ampere’s panel of 4,000 U.S. internet users.

Apple didn’t respond to a request for comment on the Ampere estimates.

In the week following the launch, Apple TV Plus had drawn “millions” of users who are spending on average more than an hour daily on the platform, Variety reported, citing sources. In addition, most viewers who watched one episode of the Apple TV Plus’ first four series — “The Morning Show,” “See,” “For All Mankind” and “Dickinson,” which have each been renewed for second seasons — went on to watch at least one more.