System Mechanic is a well regarded general maintenance tool, there's a review of it here click here . It's one of the better general purpose tools available but is it worth the money ? I don't think so, but that's just my opinion, others will think differently. I like Glary Utilities Free click here it does all I need at no extra cost.
As to will they keep your laptop "safe", that depends what you mean by safe neither of them provide anti virus or malware protection, so while useful they're not the answer to everything. As to any existing registry mechanic, there shouldn't be any problem leaving it on, just don't be too surprised if the scan results from the two products don't match.