Hi there. We have a robo and I went through all the dilemmas about the right cage. We have a Barney for our Syrian. I ended up getting the Kerry Terrarium, although would have liked the 100cm Marrakesch, pr the 100cm maxi duna multy, but didn't have space for another 100cm cage and the Kerry Terrarium is fine - I added a wood platform on legs. It is a lovely tank, but I am used to cages and find handling our robo difficult with only top access.
It might depend how tame your little guy is. If he's in a small cage like the spelos at the moment, this might be the time to get him used to being handled - they are harder to find in a larger cage
If he's quite hand tame then the Kerry would be a good option. The Duna Multy is not a bad option but I personally wanted to go a bit bigger than that.
There can be issues with robos and barred cages. 7mm bar spacing should be fine - with larger bar spacing, it isn't just escapes but I would worry they could get jammed in the bars trying to escape. The other issue is falls from a height and injuries with a cage, when they can climb bars up to roof level (or even monkey bar across the roof and drop).
When you're spending money the decision is quite important. I think you can make a larger cage a bit smaller if necessary, by filling one end with bedding as a digging area, but if you get something 70cm or so you may wish you had got something slightly bigger and want to upgrade again.
The Barney would need, in my opinion, a full level in for a robo, due to the height, even though the bar spacing is 7mm. But it could be a great cage for a robo. As with most cages, there are odd areas that have bigger gaps. With the barney it's round the doors. The top door I find needs pegging down or there's a gap under it. The two small front doors have a 1cm or more gap just below the catch. I have a row of cable ties along that bit.
I am thinking of moving our robo to a cage just because I like having a front door and thinking handling will become easier. I had the SAvic Mickey 2XL for our last Syrian and found it a great cage - it is not as tall as some and has 7mm bar spacing plus a front opening door. Although with a big door like that it might be better to have the cage nearer floor level in case a hammy made a run for it when you open the door! It is basically the same cage as the Hamster Heaven but with smaller bar spacing and without all the plastic extras like shelves and tubes (which are useless anyway - and robos can't climb tubes, they have furry feet pads).
Although the Ferplast Duna tanks don't have front doors they do have quite good access as they are very large top doors and not so tall as the Kerry.
If I could choose a cage I would either go for the Savic Mickey 2XL (80cm by 50cm and about 36cm tall interior height). Or the Barney - and make a full level for it out of wood (which could be a pain unless you're good at diy).
Tankwise I think the maxi duna multy is a good choice. Both cost around £80 to £90. I am actually thinking of selling the Kerry and gettign another Savic Mickey 2XL. The Hamster Heaven is cheaper but personally I wouldn't be happy with 1cm bar spacing for a robo.
The other advantage of 7mm bar spacing is - it's mouseproof
So if you ever get mice, they can't get in.
The Kerry and Duna tanks have small bar spacing on the lids so they are fine.
This is the Savic mickey 2xl - the wire grid shelf needs to come out - bad for hammies feet.
https://www.amazon.co.uk/Savic-Micke...ic+mickey+2+xl
This is the maxi duna multy. I think it's lovely.
https://www.amazon.co.uk/Ferplast-Ma...axi+duna+multy
There is also the Zoozone 2 which is about the same size - it's cheaper but has large 2cm bar spacing which would need meshing. Have heard the maxi duna is much easier to open and close though and the zoozone 2 lid can be a fiddle.
https://www.petplanet.co.uk/product....71&pf_id=59760
You could keep the Savic spelos - it makes a good pet carrier for vet visits! Also very useful as a small hospital cage for an old or sick hamster.