Can I connect in Luton in under 2 hours when flying BUD->LTN->KEF??

There are no connecting facilities as such at Luton Airport. You need to go through the regular arrivals immigration and go round to departures for security (plus bag drop if required).

How do you know your first flight will arrive on time?

What's your plan if you don't make your second flight?

If you don't have one or are not prepared to pay for a walk up ticket (assuming they are still available) then 2 hours is not enough time. It might be - but likely not.

I have never been to Luton, so any experience with layout and time requirements for transfers to connecting flights is appreciated. Thanks, Marco.

And thanks, ramblin' on. I appreciate a planner's mindset, but I also don't have too much choice but to rely on created itineraries sometimes. If I'm making a domestic connection with only 30 minutes between, it can be done in most airports. Even what I've read about Luton, it sounds like arriving & clearing customs & exiting the airport may take under 30 minutes up to 90 minutes in various situations. But I guess I'm more interested in what I should expect with my particular scenario.

Kiwi.com set this itinerary that allows only 2 hours in Luton, but I'm skeptical, which is why I've asked a community of wiser travelers than me.

If the community thinks this is a bad idea - trusting that I can make my connecting flight in 2 hours - then my next question would be... what should I do around Luton with 8 extra hours between flights?

Thanks again.

Looking at your itinerary, I do not get a 'warm and fuzzy' feeling.

You do not say when this trip will be, but you may wish to consider weather and the prospect of your 1st flight arriving on time.

If you have to check your luggage, you have to add retrieval and re-checking time which probably means another 30 minutes

The other issue is the wizzair check in requirement

Airport check-in starts 2 hours and closes 40 minutes before departure, according to the schedule at the airport of the place of departure. Should you fail to complete the check-in procedures by the check-in deadline, or show up at check-in or at the boarding gate in due time for any reason, we will cancel your reservation, deny you boarding and refund the amount of the total fare after deducting the relevant fees, including the Seat Protection fee.

Your 2 hours is effectively 1H 20m

Thanks, joe... Traveling in a few weeks, so of course weather could present issues. Having never flown WizzAir, I'm also not aware of just how strict they may be on baggage. If they include the handle atop my bag, they might claim it's a centimeter or two over size, or enough priority passengers may bring an overhead bin item that attendants require it be put in the hold either way.
It's great that there's such variety of low-cost airlines, but man, it'd be easier if there were some industry standards for baggage. So many variables...

If the airline staff are looking at bags, they will almost certainly be using a sizer, not a measuring tape. If the handle keeps your bag from fitting in the sizer, it is too large by that airline's standards. The handle and the wheels definitely do count. Of course, they don't always check.

Travel Update:

Luton Airport was a breeze, both for departures and arrivals. Expect 5-10 minutes to shuttle between train & airport, but that was only 2 Pounds 30, and they run consistently. I took the train starting from Covent Garden Underground on my way to LTN. I later took the train to and from St. Albans (a return ticket included airport shuttle rides) on my layover. It was all straightforward, easy, and (relatively) on time.
WizzAir did not check bag sizes on any of my flights, although I'd gotten a smaller burner bag just in case, and most people seemed to have overhead bin carryons larger than the roller bag I'd normally use for any other air travel. For the record, neither Norwegian nor WOW physically checked bag sizes/weights, either; I have heard that RyanAir is much more strict with this (and they also have very particular bag size allowances).

Departing Luton Airport (on a Sunday afternoon), I walked in, went directly to an unmanned security document scan (just set my phone down for the QR code to be read and walked through), and proceeded to the security x-ray scan line. From arriving at the airport by shuttle to arriving at my departure gate... <15 minutes ...and, oddly, not one human checked my ID or boarding pass until I was boarding.
Arriving at Luton from Budapest did require a trip through passport control, but even this only took me about 10 minutes from deplaning to bathroom through customs to the external ground transportation (if I'd had an EE/EU passport, however, I'm guessing it would've taken at least 15-30 minutes just for the passport control line). In this case, a two hour layover would have been more than enough time to transfer planes (on a Wednesday morning; I was told it is usually pretty quick), but I left the airport for breakfast & exploring in St. Albans and later departed from LTN (on a Wednesday afternoon) just as easily/quickly as I had on the previous Sunday (~15 minutes from arriving at the airport; very little human interaction or security concern).

I did not have to go to the WizzAir counter at any point; just directly through security to the gate. I also did not have to check a bag, so I don't know how smoothly baggage claim might run at Luton.