may look the same but i would be pretty certain it is not the same.You get what you pay for with diamond bits that bit may last one or 2 holes if your lucky if it even makes it through once.
It depends on what you are drilling,if you have one or 2 holes to drill in a sdmall tank with thin glass then you would probably be fine with it but if you are trying to drill a large thick walled tank then i would say buy a decent bit.
I can't tell the speed on the corded drill I use, but it's not very fast at all (how's that for a subjective answer ) I use fairly low rpms that it's fast enough that I can't gauge the rpm (IOW I can't count the rpm by staring at it), but slow enough that's it's not racing either. If I had to guess, probably a 2 - 5 revolutions a second. If it's too slow it's not really a big deal other than your arm gets tired.
If the tank is upright, I have someone spray it for me. If it's on it's side (wether by hand or drill press) I just pour a little water on occasionally. I would recommend making a template ahead of time. Usually just a simple board you cut the same size hole in as the bit you are using, then I put duct tape on the opposite side of the glass (on the inside of the tank), then clamp the template in place if it's at the top of the tank. If it's lower down, I strap it down with duct tape. Once it gets in a little, it usually doesn't move anyways unless you jerk your arm by accident.
If you are using a drill press you can build a little ring around the desired drilling location with playdough, kind of like a circular damn, and fill it with water. This way the bit is always submerged and cool. Won't work if you are drilling by hand, as you will probably want a template to guide the bit, which will get in the way.
I have 2 of them and they work just fine. I also just use water to cool the bit down. I have used one of them several times and it still cuts like a dream. I use a piece of pvc or whatever fits the bit to stop it from moving when first starting the hole.