They are basically all heat pump these days, and they should be, there seems to be no reason at all to have a condenser dryer without heat pump. Better for your clothes, better for your bills. I think it's worth paying the whatever is the small fee for instant access to Which review, or look at it at your library. Because what I noticed when I did this (at least on the version they have where I live) was that they have separate ratings for stuff like noise, whether you can change the door angle, how many programs it has etc and how accurately it does iron dry mode. I NEVER use iron dry mode - I only care about cupboard dry - that it gets the clothes dry enough. Some of them were marked down for example for making them too dry in iron dry. I don't care about that because I'll never use it anyway. I liked safety features like auto overheat switch off and where it has an alarm to remind you to empty the lint filter. The main issue is that they don't have all models, but it gives you an idea how brands are rated compared to their tests. Samsung never look good in these things - wildly variable and seem to dress things up based on the name. Siemens/Bosch are always top, Beko is a good price/performance one. I'm wary of any of the Whirlpool/Hotpoint brands and specifically avoided them.
I also find that the prices range wildly - have a look on something like Idealo with your budget max, select heat pump and then have a look what comes up, sort by price, see what brands you trust. You quite frequently find white goods on there which are supposedly discounted by massive amounts - I suspect they are rarely actually sold at the £700 price point and mostly more at the £450 mark but then get to boast massive discounts. The price history feature on there is quite useful. Obviously you need to be choosy about the retailer. I've been happy with the service from Amazon though and they are sometimes the cheapest. Or look for your local independent white goods retailer and see what they have on clearance or ex-display (often not listed online).
Apparently the energy use is so different that if you buy the exact same model in normal vs paying £100-200 extra for the heat pump version, the heat pump one pays for the difference within a year. So it might be worth investing a little more into the budget if you can squeeze it from somewhere else.
The only situation I found where it's best to stick with condenser is if it will be in an outbuilding. Heat pumps rely on there being some ambient heat from the household heating. BTW mine seems to work fine even in my kitchen which until today had a leaky window and which we don't turn the radiator on. It feels cold in there, though not as cold as outside.