(Corrects spelling of Stratasys, paragraphs 2, 8; MakerBot, paragraph 4)

By Jim Finkle

BOSTON, Nov 22 (Reuters) - MakerBot, a 3D printer maker which opened two new retail stores this week, is among the companies trying to bring the cutting-edge digital manufacturing technology to Main Street consumers, but skeptics say the rollout is premature.

MakerBot, a unit of Stratasys Ltd, opened retail stores this week in Boston and in Greenwich, Connecticut, both of which are twice the size of MakerBot's first store, 1,500 square feet in downtown Manhattan.

The company offers designs for more than 100,000 items through its "Thingiverse" online user community. The products range from knick-knacks like zombie sculptures to jewelry, sink drains and even medical devices. They are printed using its line of corn-based plastic fibers in more than a dozen colors.

"For most people 3D printing is futuristic science fiction. We're here to make it real," said CEO Bre Pettis, who cut the ribbon at the store on Boston's fashionable Newbury Street using scissors made on one of MakerBot's Replicator printers which start at $2,199.

Pettis, who has purchased splashy magazine ads to promote 3D printers as holiday gifts, believes there could soon be a 3D printer on every block in America.

Yet some technology experts say 3D printers may not be ready for prime time because they are still much less user friendly than most modern consumer electronics.

"There is so much hype," said Pete Basiliere, an analyst at technology research firm Gartner. "People are getting a little bit misled as to how easy it is," he said.

Some investors also are skeptical of 3D printing's readiness for the market. Short-seller Citron this week published an article questioning the earnings of Germany's voxeljet AG's , and shares in the sector fell, including those of MakerBot parent Stratasys and rivals 3D Systems Corp and ExOne Co.





'FRANKENHAND'

Yet stock prices don't concern Leon McCarthy, a 12-year-old from Marblehead, Massachusetts, who was born without fingers and could only afford a prosthetic hand after his dad learned that they could be made using 3D printers.

His dad, Paul, helped arrange for him to get his first printed prosthesis nine months ago, a clunky device tied together with screws, bolts and cardboard dubbed "Frankenhand."

Three iterations later, the functionality is much better, though still limited compared to devices that cost thousands of dollars. But when he broke it playing football last week, he made a new one for less than $5 on a printer at school.

Since its inception, the concept of 3D printing has drawn strong opinions. Critics say the technology could be put to nefarious purposes, like building plastic guns and other weapons resistant to detection.

But in a major vote of confidence, President Barack Obama in February singled out the industry as having the potential to create jobs and "revolutionize" almost everything we make.

Gartner says the consumer market is growing briskly, yet the numbers are still tiny compared to traditional printers. It forecasts sales will climb to some 72,000 printers next year, up from about 42,000 in 2013 and about 28,000 in 2012.

Buyers need to know that there is a learning curve, according to experts: Users must use software for computer-aided design, or CAD, or at least learn to work with templates from websites such as Thingiverse and Defense Distributed, which published the first 3D-printable gun blueprint, the Liberator.

They must also calibrate temperatures for melting plastic used to build objects, said Joe Stewart, a security researcher with Dell SecureWorks who runs a hacking space in Myrtle Beach, South Carolina, that owns three 3D printers.

"They are very finicky. You have to do a lot of tweaking of hardware and software," he said. "I'm not sure the average consumer is ready for that."

MakerBot, founded in 2009 is one of the oldest makers of desktop 3D printers, but it has plenty of competition.

The 114-page Ultimate Guide to 3D Printing, published this month by MAKE Magazine, lists more than 20 3D printers ranging in price from $399 to more than $3,000.

MakerBot's Replicator was rated best option for so-called prosumers. The UP Plus 2 from Delta Micro Factory Corp, which cost $1,649, won the "Just Hit Print" category for ease of use. The Printrbot Simple, a $399 build-it-yourself kit from Lincoln, California-based Printrbot Inc got the award for "best value. (Reporting by Jim Finkle; Editing by Richard Valdmanis and David Gregorio)