Thats only 6L mark. Although it will fire a nail, in after say 10 it will be refilling and you will be reaching for the nail punch. They don't stay at pressure. The more air you use the lower the pressure gets until it starts to refill but many of time even my 24L one can't keep up at the rate I was firing nails in, so I had to stop firing and wait, as the pressure was to low to drive the nail under the surface you then end up hitting them all with a nail punch anyway.
You want to look for 24L min for any nailer but seriously I replaced my 24L with a 50L last year and it sits in the same place under a bench, its barely used any more space up and I haven't yet had to wait for it to fill while I have been nailing.
The size of that 6L is 510 x 240 x 415mm the size of my 24L is 570x260x580mm, which is im sure you agree is nearly the same with just the added bonus of 18 more litres. My 50L is 800x300x720mm ish which is a difference but barely any more foot print. HTH
EDIT: when I first brought my first brad nailer and compressor. I was happy with it by all means but always regretted not having a 50L straight away due to the filling issue.