At the moment, it's unclear whether it's the electronic ballast that's the problem, or the tubes. Phil correctly surmised/deduced/knew/guessed that the tubes are made in China, but a lot of stuff is these days, and it doesn't all fail unreasonably soon.
After doing some research, I've become aware that there are different ways in which electronic ballasts work. The "instant start" variety are not very nice to the tubes, with the "programmed start" (a.k.a. "preheat") being rather more civilised, though taking a second or so to turn on.
Which just leaves the problem of knowing what you're buying before you buy it, given that asking the sales rep is likely to be a waste of time.
Installed 6 Nelson 28w fittings (with Nelson tubes - that have no country of origin on them) in the workshop a couple of years back to replace ageing 36w units (and cut the power bill a little). 2 are used for about 12 hours a day almost every day of the year, the others are on about 50% of the time depending on what is being worked on in that area. Never had a problem with them to date. The ends show no blackening and the light output is still excellent.
Maybe I was lucky, or the supplier Nelson used at that time was ok.
I would always recommend Philips,/ NEC tubes as in my experience they make the best T8 tubes, but at the time, the Nelson units were all I could source in a single tube T5 basic "batten" fitting, and Haymans at the time said that they had had sold a lot of them for installation in commercial premises (who they said were about the only people who used them) and had no complaints about them.
They may have been a better quality standard for commercial use via Haymans rather than for retail sale for home handyman ?
This is not to say that they are necessarily still good,
**I've used a few Nelson (CFL) lamps. Compared to Philips, I find them mechanically fragile and they take an excessively long time to warm up. I still have a couple of Nelson Par23 fluoro replacements (24 Watt) for outdoor use. Whilst they are bright (in a cold, sterile way), they take a long time to reach full light output. They have been quite reliable though. At least I'm not chugging through 300 Watts (in a double fitting) like most of my neighbours are. I've also found that Nelson 50 Watt halogen (iron) transformers are not overly reliable. Nor are the halogen fitting particularly well made. I will not touch a Nelson product again.
Agreed with the comments about NEC tubes, BTW. I use some NEC quad-phosphor tubes above my workbench. Fabulous colour rendition (important when looking at colour codes) and usefully brighter than tri-phosphor ones. The only annoying thing about NEC tubes (apart from price) is that they're available in such a wide range, that choosing the right one can take quite some time.