I've never eaten in the actual restaurant at Saffron, but I can heartily recommend their takeaways. The service has always been efficient, ready when they say, often with free poppadums or onion bhajis depending on how much you've spent, and it's good food.
With more vegetarian options than many Indian restaurants, you can make up an inexpensive feast from lots of side dishes and a couple of veggie mains. It's a really nice way to try a lot of different flavours. Persi Niramish is a good-tasting vegetable main, with a lovely name. It's sour and hot. And they do a particularly good Bhindi Bhaji (okra in a tomatoey sauce) where the okra retain a really good texture.
Perennial favourite main courses include Pathia, which isn't as hot as some, but has a good sweet/sharp balance. The Dansak is thick and filling without being too heavy. Jalfrezi and Korai are both well made, and the Birianis are good, with a nice vegetable curry (perhaps a little heavy on the celery) but not the sort of afterthought that it can sometimes be. There's also an extensive Specials list, which I have almost entirely failed to try.
Saffron seems to me a careful restaurant, which thinks about the dishes and gives them enough time. The sambar that comes with the poppadums is a case in point - a beautiful mix of sharp, tomatoey, zingy with possibly a hint of tamarind - perfect attention to detail.