Electric Die Grinders

Does anyone have experience with these? I'm in the Ryobi and Milwaukee 18v ecosystem so I don't think I want to go and add another battery system to my garage. This Ryobi Die Grinder looks like it will do what I am looking for and they say you can use a cutoff wheel with it. 
Thoughts? 

I can only speak for the Milwaukee and it's kinda turdish.  As the wheel starts to wear it picks it up as a imbalance and keeps cutting off.  I'm all about electric tools but die grinder and air hammer seem to be the two that haven't translated the best to battery power.  I would say skip the Milwaukee and give the ryobi a shot.

Good to know, I watched a comparison video and even though the Milwaukee has a higher RPM it looked like the Ryobi had more torque.

Home Depot has some good Ryobi deals of 2 batteries , charger and tool for $99 , 

You might check if the tool you want is included , 

As far as "electric" 1110v die grinders Makita were the ones you always see in shops

In reply to californiamilleghia :

I forgot they did that, I'll definitely look into if this is part of one of those deals. 
I have a bunch of chargers but it's never bad to have more batteries. 

So I did some searching on the orange home improvement store website and they do have the BOGO deal on the die grinder. $100 for 2 4ah batteries a charger and the tool. 

Worth it for the batteries alone I think. 

Personally i hate pistol grip for a die grinder, but I'm guessing air is not an option since you said electric. Have you tried a cordless dremel? 

I have a compressor but it wont produce enough CFM to keep an air die grinder useful for more than short spurts, plus compressors are loud. I have a corded dremel but I want something with a little more power behind it for removing rust off and a larger verity of attachments. 

So they were not joking when they said next day delivery, time to get some abrasive pads and put it to the test. 

Update: I have used this a few times and so far its been great. Its not the most ergonomic tool I have ever used but to me, its just as powerful as the air versions I have used in the past. The 4ah batteries last a good bit of time and I have not gotten it to stall out with Scotch-Brite pads or sanding disks on the tool. 

I will keep using it and update my findings. 

Following this as I'm also looking into the same die grinder.

If you're cheap and willing to take risks (and ignore the likelihood of false economy): I still don't have a lot of run-time on it, but so far one style of generic cordless die grinder seems promising.

I am not a paid reviewer, I do not get any kickback, I do not have a referral code, but I do have a metric bushel of caveats.
Also, Kobalt 24V die grinders are available for even cheaper.  No experience with those, there are some good ratings, but apparently they use a unique and questionable style of collet.

With coupon and/or a pseudo-discount in honor of the latest made-up 'Consumerism Holiday', this should be $80 delivered with 2x 3Ah batteries [yes I'm the one who wrote the review.  Shoulda been less than 5 stars, but 4 stars always implies the thing is utter crap]: Dufuls die grinder

Looks like the same thing under a different 'brand' w/o batteries [everything in its reviews applies to the Dufuls]: Lingyue die grinder

This thing is sorta like the way cordless tools used to be: portable and handy but not a complete replacement for a 'real' corded (or air-powered) tool.

It is usable/useful for relatively short duration jobs, like maybe 2-3minutes of continuous use, and no more than 50% duty cycle over 10 minutes (complete WAG numbers).

Buzz off a few bolts or a bracket (with a proper thin cutoff wheel, easily 3/8-1/2in dia bolts or 3/16x2in steel), or do final fitting/clearancing, or grind out short welds.  Definitely not good for fishmouthing a full rollcageworth of tube in one sitting, or porting an entire cast iron V-12.  I think you should get the cordless die grinder only if you already have a corded angle grinder.

I'm not trying to diss the cordless too much, just manage expectations.  It is seriously more capable than any 1/8in Dremel tool (speaking of, make sure to get a 1/8in collet for it... which is unavoidable b/c the only non-metric collets on Amazon are a set of 1/8+1/4). 

My biggest issue so far is that the housing gets hot FAST.  As in, too hot to hold the metal directly (however the rubber sleeve remains okay even w/o gloves).  Maybe I'm just paranoid.  I have not taken a look inside the thing to make sure there is grease.  There is some backlash (IDK if planetary reduction or some kind of spline drive) but so far I think it is not getting worse.
Long-term durability is completely unknown.  I'm sure it will not tolerate abuse, and I expect there will be no hope if anything wears out/breaks.

Finding collets to fit is not a problem (Amazon has sets, and the collets from two older HF air die grinders both fit).  IDK about a replacement collet nut, and the nut is not exactly robust (M15x1 thread + 17mm hex = theoretical 0.5mm wall thickness; nuts from the HF air grinders do NOT fit).  The included collet wrenches are extra-flimsy but any 17mm will work and the wrenches may prevent overtightening the nut.

The output torque really is impressive.  It powers a 3in x 0.095 cutoff wheel equal to any air die grinder I've ever used (zero bogging with reasonable cuts).  A 1/2" carbide burr in steel is not a problem.

Battery life is not too bad with the included 3Ah batteries (should be well over 10min at 50% duty cycle).  Running at the 2 slowest speeds, plus not continuously due to heat, helps with battery life too.  Other '21 Volt' generic batteries work, I think these are really 18V Makita style?  I have used the batteries from a SeeSii WH710 impact (the cheap mid-ish-torque which was well rated by Torque Test Channel, and seems okay from what little I've used mine).