The good news is Eaglet & Liverpool URNU are co-located, so if in the area, it's worth talking to each (Students at the URNU and Recruits at Eaglet) to see what each offers in view of your particular aims.
Both give an insight into the RN. For RNR Ratings, it'll take around five years to reached "trained status" & during that time, you are not operationally deployable but will attend a couple of marinisation & militarisation weekends at HMS Raleigh before undergoing two weeks RNR initial training, at Raleigh - usually within twelve months of joining - on average most RNR recruits get to Raleigh at about the six month stage. After this, you're then streamed into branch training. Conversely, you can achieve trained status in the RMR within about 14-18 months as a fully trained Commando.
The URNU are "List 7 Reservists" and classed as Officer cadets. They cannot be mobilised, but you can do a couple of weeks here and there on ships at sea after completing a training weekend at Dartmouth, students can undertake paid courses in UK & abroad. For example, when I was Coxswain at Oxford URNU we had students spend a fortnight flying in the backseat of FRADU Hawks & getting paid, others went to Dhekelia (Cyprus) for two weeks advance dive training funded by the service and got paid, another went on a free-fall parachute course in California, and again funded by the service and getting paid. Some students took part in shooting competitions and many went on (paid) acquaint courses at BRNC, RNAS Culdrose, RAF Cranwell, HMS Sultan, HMS Collingwood, CTC Lympstone, etc. A large number of URNU students attend the RN Ski Championships in France or this last year they organised their own URNU ski tournament, they usually attend the RN/Army Rugby at Twickenham, an annual inter-URNU sports weekend in Portsmouth and each unit has a P2000 patrol boat which accommodates 11 students and gets out to sea about two or three times a month over weekends during term time and for about a month overseas at Easter and Summer.
The URNU Mission Statement is:
"to educate a wide spectrum of high calibre undergraduates who show potential as society's future leaders and opinion formers in order to better inform them of the need for and the role in the future of the Royal Navy and to develop an awareness of the career opportunities"
RNR New Entry daily rate of pay (gross) £39.70
URNU New Entry daily rate of pay (gross) £37.10
The URNU is usually over-subscribed, the RNR isn't but, to be fair to each, it's horses for courses and they offer quite different lifestyle experiences.