Meta has launched what some are calling its "Twitter killer" app - Threads - with Mark Zuckerberg saying more than 30 million signed up in the first day.

Twitter has reportedly threatened to sue over "intellectual property rights" - with Elon Musk suggesting Meta has "cheated".

And while many are excited about a new challenge to his firm, others are not so impressed and say vital functions are missing.

Here's what users are saying needs changing.

The feed is frustrating

The home feed includes posts from people you don't follow, but who Threads reckons you might be interested in. And you can't filter these out.

Early adopters say the algorithm makes it hard to see the content they actually subscribe to and care about most.

"I've followed like 30 people and none of their post have showed up yet on my feed," wrote jimmyjxmes on Reddit.

However, Instagram boss Adam Mosseri - replying to tech YouTuber Marques Brownlee - said a feed just showing people you follow is "on the list".

Threads also doesn't allow you to order posts to show most recent at the top, the way most people scroll through Twitter.

No keyword search - and no hashtags

You can't search by specific topics eg. 'space' or 'motorcycles' - and hashtag fanatics will be #disappointed as so far they aren't supported.

Search currently only comes back with potential accounts to follow, rather than individual posts.

@FalKoopa_ tweeted: "Wait, you have no way to search posts on Threads. Bro. That's a basic feature."

There's also no trending section like on Twitter.

The ability to search properly and group together topics is so fundamental, it seems like it won't be far off.

Adam Mosseri said in a video that "more features around recommendations and trends" will be added, as well as "other features to try to improve Threads as quickly as we can".

No 'sliding into the DMs'

Some may see the lack of Direct Messaging - another core feature of Twitter - as a blessing as it cuts down on unsolicited comms.

But for others, the inability to send private messages is a big miss. Again, this could well be added soon, as Meta tweaks the app.

| Threads looks remarkably similar to Twitter. Pic: Meta

Tech companies are constantly updating their services and often put out 'rough' versions and mould them according to feedback.

It's something noted by users such as @shielddoespixel, who tweeted: "Was anyone expecting it [Threads] to be functional out the gate?

"The core is there, it just obvi needs some iteration and more work."

If you delete Threads, you delete Instagram

Meta's new baby is bound to its ubiquitous photo-sharing app - which could be a problem for anyone trying to wean themselves off it - or who doesn't have it at all.

You need an Instagram account to get started with Threads and can't just sign up with an email address.

You also can't delete your Threads profile without simultaneously deleting your Instagram account.

| Mark Zuckerberg posted about the site's first-day success

If you do want a break, there's an option to temporarily deactivate your account. This hides your profile, threads, replies and likes - but crucially your data will remain.

Threads also ties you to your Instagram username - it can't be different.

If you want to change it, you'll have to change it on both.

However, Threads does allow users to have a different bio, link, and to decide if they want their profile private.

It doesn't work on desktop or laptop

There's no web app or desktop version, meaning you can't post or scroll your feed using a desktop machine or laptop.

You'll have to download the iOS or Android phone app for that.

"If I can't type my inane ramblings on a physical computer keyboard, then I don't see the point," tweeted @BigHairyMarty.

It is, however, possible to see individual users' posts on desktop by going to threads.net and adding the username - e.g. threads.net/@skynews

It's another advantage that Twitter has over its day-old rival - for now.