Looking at the option for 2.5" drive upgrades and Samsung/Scan have some interesting price variations...

• £115 https://www.scan.co.uk/products/2tb-seagate-stbd2000102-25-94mm-sata-iii-60gb-s-25-5400rpm-32mb-cache-retail 2TB Seagate STBD2000102 2.5", 9.4mm, SATA III - 6.0Gb/s, 2.5", 5400rpm, 32MB Cache, Retail
• £90 https://www.scan.co.uk/products/2tb-seagate-st2000lm007-mobile-hdd-25-internal-hdd-7-mm-thickness-sata-iii-6gb-s-5400rpm-128mb-cache 2TB Seagate ST2000LM007 Mobile HDD, 2.5" Internal HDD, 7 mm Thickness, SATA III 6Gb/s, 5400rpm, 128MB Cache, 5400RPM
• £82 https://www.scan.co.uk/products/2tb-seagate-guardian-barracuda-hdd-25-sata-iii-6gb-s-7mm-form-factor-128mb-cache-5900rpm 2TB Seagate Guardian BarraCuda HDD, 2.5", SATA III - 6Gb/s, 7mm Form Factor, 128MB Cache, 5400rpm

That's an extra £25 for the 9.5mm with smaller cache - presumably it's a very valuable retail box.

At the same time there's an £8 saving for the silly name version of otherwise identical 7mm drives... except for the 6 grams of weight difference. Maybe it comes with an extra heavy label? :S

I'm looking for a 2TB portable USB drive (using a 2.5" drive). All major brands are cheaper than that, but I have read somewhere they tend to use the less reliable batches in external drives because they're less likely to be stressed, and therefore fail within warranty. Could be a load of rubbish though.

Portable drives are probably cheaper because they're using older 15mm drives - I've been waiting ages for them to go above 1TB with drives that actually fit.

Is there something batch-specific that makes a drive less reliable?

If there was some cost cutting factor involved then I could understand it, but otherwise my assumption would be that external/consumer drives are the ones more likely to have people bothering to claim on warranty so it'd be the other way round?

Ah, that's the wrong data sheet - the extra 6 grams on the LX001 is because that's the "hybrid" drive (FireCuda!!!!!), so it'll be the weight of the SD card or whatever it is that allows them to do their marketing bollocks. £98.50 for that extra solid magic which may or not make a few things a slight bit faster in some situations.

The other two (LM015 Barracuda/LM007 Mobile HDD) are identical weight

I got an adata 1TB usb3 about a year ago for a very good price which I promptly reformatted to ext4. No complaints thus far. It does need a powered hub for my home pc to recognize it.