I have also lived in Nyeri and we have a house there. I agree with the previous post that Nyeri is much more Kenyan than Nanyuki (which has a British military base and a large expat community). Not many expats in Nyeri, but that has never bothered me. My wife is Kenyan and I have always preferred to live away from expats. I have always been comfortable to walk around Nyeri on my own. If we want any UK food products, or nice western restaurants, we went to Nanyuki - its not very far.
Our house is adjacent to the Baptist High School, outside Nyeri itself. It's a quiet area and we have never experienced any hassle.
Ring Road Estate is the most upmarket estate in Nyeri and we looked at a few properties there. There are a few properties close to Mt Kenya Academy (Gamerock), which is a reasonably secure area.
We found that the main problem with the property market was the brokers, who seem to become involved, whether invited or not and want a % of the sale. There is inevitably more than one. In our case, we bought from a Scottish woman, who had been forced to return to Scotland by poor health. Her daughter handled the sale and refused to pay the brokers, who then threatened us. We were immediately forced to install an electric fence and eventually give them a small amount to make them go away.
Absolutely vital to spend time looking. We have bought several properties over the years and as a general rule, my wife does all the negotiating, while I remain in the background. This avoids artificially raised prices, caused by the ongoing assumption that all westerners are incredibly rich. We based ourselves at Davies Court in Nyeri, as prices are reasonable and its in a good area of the town.
With the rehabilitation of the railway, Nanyuki is anticipated to be more 'up and coming' than Nyeri, which the railway bypasses - maybe something to think about.
Schools in Nyeri: Our granddaughter, who lives with us, went to Mt Kenya Academy and this is arguably the best choice of school, in Nyeri. Its Kenyan system, but with the option to do GCSE at the senior school. She had previously attended Braeburn in Thika, a UK curriculum school. I would say that a 9 year old child would make the transition quite easily, but 12 and 14 years may struggle and may have to slot into one year below, in order to get used to the system. The Kenyan system is quite full on in terms of academic workload.
There is Brickwoods and Braeburn in Nanyuki, both UK curriculum.
One thing to bear in mind is that the UK schools on Kenya follow the UK academic year pattern, with a long break during the coldest months, whereas the Kenyan year is the reverse to this, with the academic year running from Jan to Nov.