Built in and freestanding grills
A built in grill is a head built to sit inside an enclosure. It drops into an opening in a masonry or framed island and is finished by whatever the island is clad in, and it needs that island to exist first. A freestanding grill is built the other way round, as a self contained appliance on a cart with folding side shelves and locking casters, and it is ready to use straight away.
Several ranges here are offered both ways in the same sizes, which makes the comparison direct. The decision is really about the garden, not about the cooking: a built in head is part of a structure that has to be designed, supplied and paid for around it, while a cart can be moved, taken to a new house, or put away for winter.
Grill width and cutout size
The sizes here run 24, 30, 32, 36, 40 and 42 inches, with 30 the most common. That figure describes the head itself, not the hole it goes into, and the two are not the same number.
Manufacturers publish the cutout separately, usually as its own specification sheet alongside the manual, and that sheet is what an island gets built from. It carries the width, the depth and the height of the opening the head needs, which is more information than any single number on a product title can hold. Cooking area is published separately again, in square inches, and two heads of the same nominal width can differ there as well.
Propane and natural gas
Most of these grills are described as compatible with both liquid propane and natural gas. Propane comes in a bottle and goes anywhere; natural gas comes from a line run to the spot and never needs refilling.
The practical difference is the plumbing instead of the cooking. A natural gas grill is fixed where its line is, which suits a built in island and is a reason to settle the fuel before the island is built. A propane grill on a cart has no such constraint. Which conversion a specific model needs, and who is allowed to carry it out, is set by the manufacturer and by local rules.
Stainless steel construction
Nearly everything here is stainless steel, inside and out. That is not a styling decision: an outdoor cooking appliance sits through rain, frost and salt air while being repeatedly heated to several hundred degrees, and few materials tolerate that combination.
Where products differ is in the grade of steel and the thickness of it, and the parts where that matters most are the ones nearest the flame: burners, heat diffusers and cooking grates take heat and corrosion together, so they age faster than the cabinet around them. Those are the components to compare on a specific product, and in this category they are also the parts makers most commonly supply as replacements.
Burners and BTU
The larger heads here publish figures around 60,000 BTU and upwards, spread across several burners, while the compact ones are correspondingly lower. The total on its own says less than how it is divided, since what makes a grill easy to cook on is being able to hold different temperatures in different parts of it at once.
Features that repeat across the range include infrared sear zones, rotisserie burners and interior lighting. Each answers a particular way of cooking: a sear zone for steak, a rotisserie for whole birds and joints, and lighting for anyone who cooks after dark.
The grill in an outdoor kitchen
A built in head is one component of an outdoor kitchen, and it is usually the one chosen first because its cutout sheet sets the dimensions everything else is fitted around.
The outdoor kitchens range covers those components, and outdoor kitchen islands covers the structures themselves. If the plan is a stone clad island, the granite slab page covers a surface that takes outdoor conditions.