As said in posts above Wickes and Benchmarx are both Travis Perkins group companies. Benchmarx operates similar to Howdens in being “accounts” based and Wickes acts like the “retail” side. The kitchens are the same kitchens. With Benchmarx they are just supplied pre-assembled.
In my experience Howdens are a slightly lower quality product. Their carcass and worktop (laminate) materials are amongst the poorest quality. Search fitters or trade forums and you will find fitters complaining about how the rubbish they put in them kills their blades, router cutters etc. I’ve even seen mention of metal bits in their chipboards something that would not happen with the QC procedures in place at companies like Egger, Krono and Deco.
Also, their melamine is usually thinner and chips easier too (certainly true of Ikea laminates) making cuts unsightly. Although in this regard and in fairness to Howdens, I suspect none of the big brand names use boards and melamine at the Egger, etc quality level.
Be wary of companies calling their cabinets “rigid”. Lots of places from, Benchmarx to Units Online, are saying they supply “rigid” units because they are supplied pre-assembled. However, what many actually supply is a Cam and Dowel unit. This is a pre-assembled flat pack unit. Basically, an Ikea unit assembled prior to delivery.
Note that in delivery, handling, expansion and contraction of the timber based panels, vibrations caused by dishwashers etc, cams will loosen and with this the units lose what rigidity they first had. This will obviously impact the overall look of the kitchen as doors lose alignment, in-frame doors will bind on their frames etc.
True rigid kitchens are built using cabinet making techniques that result in a rigid and robust structure that will resist racking (as much as any open box unit can). Racking is the horizontal movement that causes a rectangle to deform into a trapezoid shape which is thus out of square.
Properly built rigid units will not lose square. Building a truly rigid unit could involve any or a mixture of glue and dowel, lose tenon joinery, housing joints such as dadoes or rabbets, glue and screw, box joints, etc.
The vast majority of rigid units are usually glued and dowelled (with many more dowels than you’d have cam joints). Rigid units, of any variety, also get their strength and rigidity from the use of optimal, evenly distributed pressure, applied across entire cabinet joints (eg by machine presses) as the glue cures rather than the low amount of point only pressure provided by Cam fixings.
As is unfortunately always the case, not all truly “rigid” units are made equal. Any open box design cabinetry will have a tendency to “rack” (ie move horizontally from left to right making a trapezoid shape rather than a perfectly square rectangle).
The only way to truly “cure” racking, if not reduce it to a negligible amount, is with diagonal bracing on the rear of the unit. A solid back panel achieves this, provided it is properly jointed when building the unit. It is also more sightly than 2 tensioned diagonal metal straps from corner to corner.
BUT, for the rear panel to effectively add rigidity and counter racking it needs to be securely fixed. With most production kitchen units being made with MFC panels this is best achieved with glue and dowel construction where ALL cabinet components are glued and dowelled together making one solid homogeneous piece of furniture. The very best quality MFC based units are made like this - ie 18mm boards on ALL sides of ALL units (ie wall, base, etc), glued and dowelled together. As a side note, with birch plywood based carcasses glue and screws, preferably with (but even without) housing joints, will also work very well as ply takes screws much better than chipboard.
In spite of this, many manufacturers cut production costs by using thinner backs. These thinner backs can only be slid into slots (mostly loosely and so adding no rigidity) or be stapled on (again adding no strength or rigidity to the unit). This is why even manufacturers advertising glue and dowel construction are not all making the same quality cabinet.
My understanding is that DIY Kitchens used to make wholly 18mm units with all pieces glued and dowelled. This is certainly no longer the case (just checked their website) as they use thin backs which are too thin to use dowels. They’ve also stopped using PWS and Burbidge kitchen components which they always made a point of advertising in the past (certainly when I first heard of them) - it would be interesting to know whether this was also a decision made to reduce production costs.
Anyways after the long rant I’d rate the units mentioned by the op as:
- DIY Kitchens
- Units online (marginally in front of)
- Wickes/Benchmarx (I prefer the pricing transparency of Wickes to the Benchmarx/Howdens model and with sales and a reasonable fitter Wickes can often work out cheaper for the same kitchen).
- Howdens, B&Q, etc etc
Incidentally, cam fixings are generally called “knock down” fixings (designed so that furniture can be non-permanent and easily disassembled) so consider this when a retailer states that a Cam and Dowel construction is “rigid” and as good as a “glued and dowel” or other truly rigid built unit.
PS - I can’t comment on Magnet - anything I’ve heard is hearsay and not something from personal experience.