But observers suggested the tech giant's decision to introduce a budget device "could well be the trump card needed to trounce Android's hand".
Stuart Miles, editor of gadget website Pocket-Lint, predicted the cheap device would be snapped up but could be viewed as a new take on an earlier iPhone.
"The 5C is obviously a device that is aimed at being a lot more colourful and youthful and designed to appeal to a global market," he said.
"I think it will sell incredibly well however those that want to criticise it will say that ultimately it is a souped up version of the iPhone 3G."
He predicted the 5S would also become a popular handset at a time when "nobody else is doing fingerprint scanning".
"There are no gimmicks here - you'll use the scanner even if it's just to unlock your phone."
Adrian Drury, an analyst a research firm Ovum, branded the high-end model a "halo device designed to set a new bar for mobile computing".
"While the IPhone 5C is the new lower cost device in the range, Apple is at pains to stress its quality and power," he said.
"This is a device designed to revolutionise smartphone market shares."
Meanwhile he said the faster 5S would "set new stakes for gaming on a smartphone" while the security sensor ensures iTunes purchases are "now just a fingertip away".
Ernest Doku, of comparison uSwitch.com, also hailed the advanced model, adding the Apple's "rock-bottom" pricing injected a "modicum of surpass" into its latest announcements.
He added: "Apple's never had an offering for the mid-range smartphone market, leaving Samsung - with a phone for every budget - to clean up. The 5C could well be the trump card needed to trounce Android's hand."
Jason Jenkins, editor of technology site CNET, said Apple has made a play for the "geeks" it "lost" to Android with the 5S.
"Android phones like the Samsung Galaxy S4 and HTC One are known for containing very fast processors, while iPhones have been left behind," he said.
"By using a technology called 64-bit processing, Apple is hoping to leapfrog the competition and attract the high-spending, nerdy crowd that like owning a phone that is technically faster than everyone else's."
He said the plastic iPhone 5S "looks to be a good buy" but was "nowhere near as cheap as we were hoping for".
The handset costs 99 dollars (£63) with a two-year contract or £469.
Stephen Ebbett, global director of gadget insurer Protect Your Bubble, warned earlier models that have sported fingerprint scanners have proved temperamental.
"Apple's budget iPhone is a first for the manufacturer that, until now, has offered only top-of-the-range handsets," he said.
"Although the 5C is Apple's attempt to grow its customer base in the developing markets, it could well be the younger audience that buys into the budget device - firstly, because it comes in an array of fun colours, but also because this phone is practically teenager-proof with its tough steel frame and polycarbonate body.
"As rumoured, Apple's iPhone 5S introduces Touch ID, using touch-based fingerprint sensors - but this could turn out to be more a gimmick than an impenetrable security measure at this stage.
"Being able to use fingerprint security login for iTunes purchases is a nice touch, if it works. And with the rise of wireless payment technology, the mobile space is crying out for better security.
"But while biometrics are typically seen as more robust than password protection - sweat, dirty pockets, hot and cold environments, sun exposure, and other factors can affect the sensitivity and working conditions of the sensor surface."