Hi James, welcome to the froum
Pre-facelift designations are SE, ES and EX, with a '-T' denoting Sat nav on the lower two trim levels (EX has nav standard).
I personally wouldnt go for a SE, as they have low spec (no cruise control especially). Thus a good ES from 2010 on would be a good choice.
Factory nav is average at best - depends if you really want it in the dash. Cheaper to buy a facory nav car than fit it later, but using a Tomtom or similar is likely more effective. The nav does not have reversing camera like the Prius, so also a consideration - and I believe the factory nav unit (made by Clarion) has poor FM reception.
No electric only, as IMA doesnt work like HSD. The car is lighter and slightly more traditional car-like than a Prius, with typical Honda handling (a good thing). Compared to the Prius 3, you could expect about 4mpg equivalent less on average. Urban 40 or so, motorway 55-68 or so. Road tax £10. It has an Eco mode button, which I find produces a jerky ride in town, thus I only use it on the motorway, and I take the 4-5mpg loss. Seat heaters on ES and EX result in a loss of 2-3 MPG per seat while on.
Things to watch out for: regular servicing by dealer almost a must, as the IMA system is warranted for 8 years with service history. The car needs CVT oil replaced every 2 years (a must). The car has 2 spark plugs per cylinder (8 total), and these are expensive and tricky to fit the rear bank I believe - they need changing at 100K or so I believe.
No other problems reported really, batteries, gearbox are all trouble free.
Get an ES without Nav with less than 60K, and you'll have a good car. Watch out for accident damage, as they are light and damage easily.
They are temperamental to a failing 12v lead acid battery, so note that too - that's a simple replacement at 5 years or so.
Crap in ice and snow on stock tyres.
The arm rest between the front seats is too low, and doesnt provide an elbow rest, and the cup holders are scarce and awkwardly placed. Rear vis can be poor at night, as the bar that splits the two rear winscreens can obscure the headlights of drivers behind.