My experience with the regular "golden" series is better than with the SK series. I have (had) 5 smaller ones and 2 larger ones. The larger ones I have replaced with Hacker, sorry I don't trust the magnets even after putting CA glue.</p>

On the smaller ones no problems with magnets but shaft is relatively soft. The bearings are not of the highest quality either and if the prop is not absolutely  perfectly balanced u will have problems with them.</p>

On the other side 4250-700 and 4240-1050 are performing very good in Element 30 and Acromaster.</p>

Just don't push it to the max power suggested by HK, up to 70% is fine.</p>

Where do you plan to use this motor, may be I can help you choosing a better one?</p>