I have one. There are two variants, that have different spend levels and reward levels (Avios per pound spent). You also get a 241 for Avios flights voucher if you spend enough in a year, how much is enough depends on the card variant. One is free, one is £150 a year. IMO the £150a year isnt worth it unless you spend a lot. You'd have to do the maths, work out what £150 would buy you in miles and then compare that to the extra Avios you'd earn at 1.5 compared to 1 per pound.
When you get one make sure you get it from an offer than gives you bonus Avios to start with.
As TP says, set your expectations correctly though.
Here are the downsides;
Part miles, and certainly all miles, for economy flights, is a complete waste of Avios. Literally.
You also cannot use them (in practice) to upgrade economy to PE.
Best bang for buck is PE to Club upgrade (means you have to buy PE seats.
The route to LAS is very popular, so availability is thin on the ground, you need to book a long way in advance. TP advises looking at going to SFO but IME thats even worse :-)
However, there is no downside to getting one if you get the free one, its 3,000 Avios 'for free' plus any extra Avios earned on spend.