Addis is high, so watch out for your performance/payload. And gets some rough weather at times. I'm not sure what Wx is doing at the moment, but its not a nice place to come into at night in bad weather. Its pretty pedantic too.
JKIA is fine as a tech stop. Its bureaucratic/expensive (where isnt in Africa). Its undergoing redevelopment so parking, procedures are a bit chaotic. Parking also gets pretty congested when the national airline comes home to roost at night, but midday its okay. There are however a couple of remote/GA parking areas for visiting aircraft. Fuelling can be by bowser or underground tanks, but you need to specify what you want to Ground frequency so they can relocate you as necessary. Its probably best to use the 'semi-official' handling agent (Tradewinds) to handle you to save a lot of running around - clearances/fees/flight plan etc. JKIA is 5,500' altitude, and temps are currently around 30's - but the runway's plenty long for most airplanes.
If you're just stopping for fuel etc, JKIA is fine but a long way from town/hotels for anything else. If you're night stopping the nearest hotel is outside the airport, halfway to town in chaotic traffic. You need to allow plenty of time to get in/out through all the airport procedures. Watch out you have current airport diagrams - parking bays are recently renumbered which are not always on the international databases.
Oh and the rainy season is currently heading northwards towards Nairobi at the moment. Should be here anytime in the next month - so CB's, thunderstorms, plenty of rain and tops around 40,000'. And not a lot of help from ATC at times....
Good luck.