What I myself would do is ask the person doing the build what they think are the advantages to having it on a slide. Maybe that person has valid points for suggesting it should be on a slide that you need to consider in your decision making. You are working in partnership with that person so ask that person first, then validate if the answer does not seem to make sense to you.
My fridge is on slides as I could not open the top otherwise. But there are two other reasons for the slide, easier access to the wiring on the wall behind its where it is plugged and on hot summer days I leave it pulled out so there is less heat build up inside the cabinet. I do have ventilation on the cabinet door and sides, a must do for units that produce heat but it is better for the electronics and compressor that it has even more air circulation on really hot days. But fridges of course have another reason for keeping the temperature around them lower, they do not have to cycle on as often. So my answer is not quite a direct comparison in all the functions for my choosing slides.
Still your Bluetti does produce heat so the cabinet does need some type of venting to reduce heat build up inside the cabinet. I have a decorative, perforated aluminum panel in my cabinet door and also on the end panel of the side of that cabinet. Even my solar charge controller has cooling fins on it so it too is in a small cabinet that has perforated panels to allow for air circulation to reduce heat build up. I am my own designer and builders so I had to think through all of that essential air circulation stuff to keep my electronics and wiring safe from excess heat through before I started my build. Talk to your builder, listen to their explanation.
