I have a Samsung UE32ES5500 which I bought about a year and a half ago.
The two deciding facilities it had were a USB PVR and a web browser.
I hooked up a 2TB Seagate USB3 drive and it seemed fine, recording scheduled programs from standby even in HD. The web browser also seemed reasonably quick.

Then the irritations started. About once a week the TV would decide the USB drive wasn't connected any more and not record anything scheduled (and yes the hard drive has a seperate power supply).
The web browser crashes every few minutes even when just looking at mainstream pages from say Google news.
If the TV is recording a program then the smart hub and browser won't connect to the wifi, you have to stop the recording then it's fine.
Every other day the smart hub decides to spend 10 minutes updating before it or the browser can be used.

Is this typical of earlier smart TVs? Does this happen with other brands like Panasonic and Toshiba? (I notice Finlux use the Opera browser which I guess is fairly stable).

I've got a 2011 Samsung UE40D6530 Smart TV after waiting for a TV with a good picture and Smart to be available, and I use an Hitachi Portable USB 320GB hard drive (not mains powered) that I had spare, which does the job of recording TV progs. I've never had any problems with it.

I eagerly tried the web interface but it was totally useless using the remote so only gets used rarely for Youtube, and even then it's a pain entering the text. The problem you are facing is the CPU in the TV is too slow so buffers all the time, I reckon.

As you say they are not reliable and usually supported firmware wise for about 18/24 months before the manufacturer moves onto a new improved Smart TV platform. Not a great idea to record directly onto a hard drive either unless you keep up to date with those recordings as they can only be viewed on that particular TV.

Always better to get a dedicated box for streaming/media playback and a PVR as it will cause you a lot less problems in the long run. A lot of the new Samsung range use quad core processors so they may have improved speed but reliability will always be an issue as they are trying to cram too many features in ...

I believe even the latest bunch of smart TVs are going to disappoint a lot of people. They are trying to emulate a computer with a TV tuner added when in fact thy are a TV Tuner with a very low powered set of computer type components added. Until they have quality processors, memory etc inbuilt they are never going to replace even a moderate PC or tablet for browsing and certainly not a good PVR for its functionality. You don't buy a Ford Mondeo fitted with off road tyres and expect it to climb a mountain so why expect a relatively cheap TV to do something it hasn't been designed for.

I got a Sony smart tv for the bedroom and, frankly, won't bother again. As has been said, they tend not to be particularly great at what they do, but the clincher for me is the lack of ongoing support. My model was (just) pre-netflix and Sony decided that they weren't going to add it as it'd be technically too hard / impossible. If I'd just got a £30 dongle (e.g. Chromecast) I'd have just shrugged my shoulders and bought another which CAN support it. It's a bit harder to do that with several hundred pounds worth of TV though.

So sure, if it's on the model you want anyway, why not? But I certainly wouldn't let it influence my decision again.

A few years ago when freeview first came out TVs with intregrated freeview came out but as freeview developed a lot of TVs did not handle updates or worse manufacturers did not bother updating.

Smart TVs will suffer same way perhaps worse as ongoing development.

Buy a good dumb TV with multiple HDMI inputs.
Buy the smart part separately and upgrade as technology develops. This will be fraction of a smart TV cost