Woo a car on here I can actually talk about!
I've got one of these, it's still my first car, had it for 6 years.
In that time not much major has gone wrong with it. They have an issue with exhausts rusting through at one point, I'm on my second replacement but this time the guy replaced the whole lot so hopefully it's good for quite a few more years. It was only £70 from an independant though! It's overheated twice, once was water pump, the other was thermostat iirc. It's had new front discs and pads... that's about it!
So in 6 years of motoring, no services, it's cost probably about £400 to fix. I'm pretty happy about that.
The interior feels fairly solid to me. Whilst it's a bit bland, I prefer it to most of the bendy plastic alternatives that my friends have. The stock speakers are ok... Loads better than my sisters punto anyway! I also like the driving position, I find it pretty adjustable which is great as I was having difficulty in other cars when I was looking (I'm not that tall, 6'2)
Why are you going for a diesel? Mine is a 1.4L, 3 door, certainly not quick but it feels nippy about town. Bit noisy on motorway. I would go for a five door if i had the choice again. The 3 doors are really heavy, too big, and swing away from you if you're not careful. I keep grounding it on high kerbs.
Not loads of room in the back but it's better than some! I get more head room in the back of my car than others, which is my main issue with being in the back of little hatchbacks. Boot space is good
I'd say go for it. They seem like pretty solid little things to me (in my limited experience!)