It looks like the Janome model that you identified earlier, but without the extra gathering foot.
As a general rule, I think places like Costco are good value for electricals. The only caution I would give is that if anything goes wrong, the chances are they will only be able to give a refund or possibly send it away for repair.... they are unlikely to be able to replace it because the stock turnover is so high. If you bought from a sewing machine shop or one of the reputable online suppliers, you'd have access to ongoing support and possibly an extended warranty.
My general rule is to use Costco/Makro etc for smaller/cheaper electricals where I'm happy that I will feel I have had good value if it lasts the year or so it is guaranteed, and that anything else is a bonus. At nearly £200, I'd be more hesitant, but that's just me.
If I were buying again, I'd go for this SMD-badged Frister at £199:
http://sewingmachines.co.uk/SMD_over.htm. The advantages over the Costco Janome are:
- a 2-thread converter for very fine rolled hems
- the front of the machine opens up completely for easy threading (a huge issue with many overlockers)
- a 5-year warranty with paid courier collection and return in the event of a claim
- 12 free large cones of overlocker thread, a set of Frister scissors and a carry bag as standard free gifts
I have a branded Frister from SMD (without the 2-thread converter, sadly) and it is a very solid, reliable machine that I enjoy using.
