Mobile app marketing costs and download volumes for the top 200 apps in Apple’s App Store saw year-on-year increases in March, according to app engagement company Fiksu.

Fiksu’s cost per loyal user index increased 4.8 per cent to $1.36, compared to $1.30 in March 2012.

The Fiksu app store competitive index — the average aggregate daily download volume of the top 200 free US iPhone apps — was 12 per cent higher than March 2012 at 5.02 million.

Compared to the prior month, the cost per loyal user index in March 2013 rose 5 per cent while the app store competitive index fell by 4 per cent, from 5.2 million.

Micah Adler, Fiksu’s CEO, said the healthy inventory with relatively steady costs reflects “a maturity in the overall quality of apps and their ability to engage users”.

But he warned that despite the steady recent months, marketers must always be prepared for the “ebbs and flows that inevitably happen in the complex app ecosystem”.

In its analysis, Fiksu said Apple’s decision to no longer accept new apps or updates that access Unique Device Identifier (UDID) technology, as well as its changing stance on apps promoting other apps, may have an impact on the April figures.

The Fiksu Mobile App Marketing Platform recorded its one-hundred billionth app user action in March and has now driven more than one billion app downloads.

Adler recently told Mobile World Live that effective attribution of downloads is becoming a major challenge for iOS app marketers.