I am planning to get a Neutral Density Filter for one of my lenses (58mm filter lens). But I am new to filters and clueless on the parameters to check for before I could select one. I recently stumbled upon one: Polaroid Multi-Coated Variable ND. Can someone share the parameters to look for while buying an ND filter? and preferably reviews of the above mentioned product - don't know if I could ask for reviews here, but I could not get better reviews from anywhere else!
The item you linked to already has three product reviews on Amazon. I can't specifically comment on that one since I have never used it, but I have no reason to believe that it wouldn't be satisfactory for basic uses. It is a variable neutral density filter, which is a bit different then what you specifically mentioned in the question(since I think you implied a solid ND filter).
We have a great blog post already about high quality variable neutral density filters, take a look at this: http://photo.blogoverflow.com/2012/03/marumi-nd2-400-variable-nd-filter-review/
We also have many questions that will help you, see:
One thing to consider is any other lenses you may own, now or in the future, may be larger than 58mm. Unless you're happy to buy other ND filters at the larger sizes, you may want to consider buying one large size (72mm or 77mm) and then using a step up ring. For example if you buy a 77mm ND filter, you buy a 58mm-77mm step up ring for this lens, and other step up rings for your other lenses. The step-up rings are a few dollars, so far cheaper than buying separate ND filters for each lens.
Concerning the ND parameter:
ND2: Passes 50% of the light intensity (1 step). Therefore, to achieve the same exposure had no filter would require a doubling of the exposure time.
ND4: Passes 25% of the light intensity (2 steps). Should be multiplied x4 exposure time.
ND8: Leave spend 12.5% of the light intensity (3 steps). Should be multiplied x8 exposure time.
ND16: Passes 6.2% of the light intensity (4 steps). Would have to multiply x16 the exposure time.
ND32: Leave spend 3.1% of the light intensity (5 steps). Would have to multiply x32 the exposure time.
ND64: Passes 1.5% of the light intensity (6 steps). Would have to multiply x64 the exposure time.