Great budget choice in Nairobi. They had a range of options, but I stayed in the cheapest option which was a shared dorm costing about 13 USD per person per night. Breakfast was included in the room cost. They also offered a dinner buffet at 7 p.m. everyday for Ksh 700. If you don't care for the buffet (the vegetarian options aren't that great) and can't eat at 7, you could order off the lunch menu any time. The restaurant and bar stays open until at least 11 p.m.
The guesthouse is in a convenient location and has pretty decent security, although you should exercise caution walking around anywhere in Nairobi, particularly after dark. You can buy pretty much everything you need, from toiletries to a Kenyan SIM card, within a few minutes' walk from the guesthouse.
Wildebeest also have a number of taxis associated with them and they can arrange for pick-ups and drop-offs to the airport or elsewhere around town. They cost a couple of hundred shillings more than you'd pay if you got a taxi yourself, but then again, you have the security of knowing that the taxi driver is legitimate and they're pretty friendly too.
The best thing that I liked about Wildebeest is that they were willing to store your luggage. So if you wanted to take a short trip around Kenya (whether it was organized through them or you were doing it on your own), you could leave some of your luggage there for a week or so without dragging it everywhere with you. That was very helpful if you didn't need some luggage and would prefer not hauling it in matarus, tuk-tuks, and bota-botas when you didn't have to.